docs: sync API reference updates with Docusaurus on integration releases

[anakin87]

Related Issues

• part of https://github.com/deepset-ai/haystack-private/issues/132

Proposed Changes:

• introduce a workflow to update API reference on Haystack when a new version of a core integration is released

Design choices

• Use peter-evans/create-pull-request action which is robust and works well
• Follow recommendation in [Help needed] Copy a file from one repository to another by submitting a PR peter-evans/create-pull-request#1304 (comment)
  • Create two separate jobs: one for API reference generation, the other one for creating a PR in Haystack. This works well because peter-evans/create-pull-request works on the repo corresponding to the preceding actions/checkout.
  • Use artifacts to temporarily store the generated markdown files. Artifacts are free for public repos.

How did you test it?

Tested on this PR. Here is an example PR created: deepset-ai/haystack#9917

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[dfokina]

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