Create IR structs, and merge functions for IRs.

[sawsa307]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Add structures needed to support translation of extension features.

Which issue(s) this PR fixes:

Fixes #125

Does this PR introduce a user-facing change?:

None

[sawsa307]

/assign @LiorLieberman

[LiorLieberman]

I appreciate you put the time to split this to two more concise commits. This is very useful, thanks @sawsa307 !

[LiorLieberman]

This Looks good to me, thank you so much for all your hard work @sawsa307 💪!

/approve
lets get final lgtm from @robscott for the specific logic

I also tested it locally with two files.
one is:
./ingress2gateway print --input-file tmp.yaml -A --providers gce

tmp.yaml

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: sa-test
  annotations:
    kubernetes.io/ingress.class: "gce"
spec:
  rules:
  - http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: whereami
            port:
              number: 80
---
apiVersion: cloud.google.com/v1
kind: BackendConfig
metadata:
  name: sa-test
spec:
  sessionAffinity:
    affinityType: "CLIENT_IP"
---
apiVersion: v1
kind: Service
metadata:
  name: whereami
  annotations:
    cloud.google.com/neg: '{"ingress": true}'
    cloud.google.com/backend-config: '{"default": "sa-test"}'
spec:
  selector:
    app: whereami
  ports:
    - port: 80
      protocol: TCP
      targetPort: 8080
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: whereami
spec:
  replicas: 3
  selector:
    matchLabels:
      app: whereami
  template:
    metadata:
      labels:
        app: whereami
    spec:
      containers:
      - name: whereami
        image: bla/whereami:v1.2.20
        ports:
          - name: http
            containerPort: 8080
        readinessProbe:
          httpGet:
            path: /healthz
            port: 8080
            scheme: HTTP
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  selector:
    matchLabels:
      purpose: bsc-config-demo
  replicas: 2
  template:
    metadata:
      labels:
        purpose: bsc-config-demo
    spec:
      containers:
      - name: hello-app-container
        image: bla/hello-app:1.0

output:

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  creationTimestamp: null
  name: gce
spec:
  gatewayClassName: gke-l7-global-external-managed
  listeners:
  - name: http
    port: 80
    protocol: HTTP
status: {}
---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  creationTimestamp: null
  name: sa-test-all-hosts
spec:
  parentRefs:
  - name: gce
  rules:
  - backendRefs:
    - name: whereami
      port: 80
    matches:
    - path:
        type: PathPrefix
        value: /
status:
  parents: []
---
apiVersion: networking.gke.io/v1
kind: GCPBackendPolicy
metadata:
  creationTimestamp: null
  name: whereami-GCPBackendPolicy
spec:
  default:
    sessionAffinity:
      type: CLIENT_IP
  targetRef:
    group: ""
    kind: Service
    name: whereami
status: {}

Second test to previous capabilities not break:
./ingress2gateway print --input-file ingress.yaml -A --providers ingress-nginx

ingress.yaml

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: example-ingress
spec:
  ingressClassName: nginx
  tls:
  - hosts:
    - foo.example.com
    - bar.example.com
    secretName: example-com
  rules:
  - host: foo.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: foo-app
            port:
              number: 80
      - path: /orders
        pathType: Prefix
        backend:
          service:
            name: foo-orders-app
            port:
              number: 80
  - host: bar.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: bar-app
            port:
              number: 80
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: example-canary-ingress
  annotations:
    nginx.ingress.kubernetes.io/canary: "true"
    nginx.ingress.kubernetes.io/canary-weight: "50"
spec:
  ingressClassName: nginx
  tls:
  - hosts:
    - foo.example.com
    - bar.example.com
    secretName: example-com
  rules:
  - host: foo.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: bar-app
            port:
              number: 80

output:

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  creationTimestamp: null
  name: nginx
spec:
  gatewayClassName: nginx
  listeners:
  - hostname: bar.example.com
    name: bar-example-com-http
    port: 80
    protocol: HTTP
  - hostname: bar.example.com
    name: bar-example-com-https
    port: 443
    protocol: HTTPS
    tls:
      certificateRefs:
      - group: null
        kind: null
        name: example-com
  - hostname: foo.example.com
    name: foo-example-com-http
    port: 80
    protocol: HTTP
  - hostname: foo.example.com
    name: foo-example-com-https
    port: 443
    protocol: HTTPS
    tls:
      certificateRefs:
      - group: null
        kind: null
        name: example-com
      - group: null
        kind: null
        name: example-com
status: {}
---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  creationTimestamp: null
  name: example-ingress-bar-example-com
spec:
  hostnames:
  - bar.example.com
  parentRefs:
  - name: nginx
  rules:
  - backendRefs:
    - name: bar-app
      port: 80
    matches:
    - path:
        type: PathPrefix
        value: /
status:
  parents: []
---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  creationTimestamp: null
  name: example-canary-ingress-foo-example-com
spec:
  hostnames:
  - foo.example.com
  parentRefs:
  - name: nginx
  rules:
  - backendRefs:
    - name: bar-app
      port: 80
      weight: 50
    - name: foo-app
      port: 80
      weight: 50
    matches:
    - path:
        type: PathPrefix
        value: /
  - backendRefs:
    - name: foo-orders-app
      port: 80
    matches:
    - path:
        type: PathPrefix
        value: /orders
status:
  parents: []

[LiorLieberman]

/label tide/merge-method-merge

[robscott]

Thanks for all the work on this @sawsa307 and also to @LiorLieberman for the great reviews!

/lgtm
/approve

(For future readers, most of my review for this work was actually on #185.)

[k8s-ci-robot]

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