Add process applications feature

[philippfromme]

Proposed Changes

Backend

• adds file-context feature
  • all open files are added to file context
  • metadata is extracted from every supported file type (.bpmn, .dmn, .form, .process-application)
  • process application is opened/closed automatically if opened/closed file is part of process application
  • opening process application watches process application directory

Frontend

• ProcessApplications feature to open and close process applications automatically
• new application menu entry to create process application
  • choose directory, empty .process-application file will be created

• new (➕) entry to create process application
• works the same as new application menu entry

• new button in status bar that is shown when open file is part of process application

• new overlay that shows all files that are part of same process application as open file

• different tab header for files that are part of process application

Try it out

I've added an example process application: a354d21

Open any file in this directory to see the process application.

To run the Camunda Modeler try npm install && npm start

Follow-ups

• References feature to get reference from and to resources
• AutoCompletions feature to get autocompletions
• Branch: https://github.com/camunda/camunda-modeler/tree/references-autocompletions

Closes #4666
Closes #4675
Closes #4687
Related to #4676
Related to #4664

Checklist

To ensure you provided everything we need to look at your PR:

• Brief textual description of the changes present
• Visual demo attached
• Steps to try out present, i.e. using the @bpmn-io/sr tool
• Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}

[nikku]

This will be used (again) once we support "endpoints" for deployment.

Why would we remove it here?

[nikku]

(Of course fine, if we consider to store the endpoints in a different place, once supported).

[philippfromme]

I removed it because it's not used at all at the moment and was probably meant to be removed. I would rather reintroduce it again in the context of adding a feature that requires it.

[nikku]

We just have to be aware that this is "the data model" that was previously used. We can remove it, but then we'll not remember the data model once we re-introduce an endpoints feature.

[nikku]

@philippfromme Please add "steps to try out" to this PR, so @lmbateman and others can give it a run (to understand the UX we propose).