docs: sync API reference updates with Docusaurus on release

[anakin87]

Related Issues

• part of https://github.com/deepset-ai/haystack-private/issues/132
• similar to docs: sync API reference updates with Docusaurus on integration releases haystack-core-integrations#2433

Proposed Changes:

• add Docusaurus config files
• introduce a workflow to update API reference on Haystack when a new version of Experimental is released
• this is different from the current (erroneous) logic for Readme. For Docusaurus:
  • we only update API reference with the release
  • we update all versioned API references (as we do for integrations)

How did you test it?

Tested on this PR. Here is an example PR created: deepset-ai/haystack#9921

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:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 18743237328

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 71.165%

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Totals
Change from base Build 18741290601:	0.0%
Covered Lines:	1118
Relevant Lines:	1571

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💛 - Coveralls

[dfokina]

LGTM