Added info about EKS Pod Identity as an authentication mechanism

[yurhasko]

Description of your changes

Fixes #1529.

Added documentation for EKS Pod Identity as an authentication mechanism for provider-aws.

I have:

• Read and followed Crossplane's [contribution process].
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

I did the testing on an EKS cluster myself, because there was a need to configure EKS Pod Identity for Crossplane, and since no info was present in the documentation, I used some examples #1459 alongside with my own additional configuration

[mergenci]

Thanks for your contribution @yurhasko 🙏 Documentation contributions are among my favorite 😎 I haven't read it yet, but can you have a quick look at https://github.com/upbound/configuration-aws-eks-pod-identity and see if it has any useful material that we could use in the documentation?

[yurhasko]

Thanks for your contribution @yurhasko 🙏 Documentation contributions are among my favorite 😎 I haven't read it yet, but can you have a quick look at https://github.com/upbound/configuration-aws-eks-pod-identity and see if it has any useful material that we could use in the documentation?

As far as I can tell, the doc that you provided describes creating Pod Identities for other applications via Crossplane (which I wasn't aware of, thanks, that looks cool). My addition to the authentication doc describes using Pod Identity as a way of initial authentication configuration for the AWS Crossplane providers, so I think that it serves a different purpose