docs: Add documentation for AlloyDB doc store and retrievers

[bogdankostic]

Related Issues

• partially addresses Alloydb Integration haystack-core-integrations#1749

Proposed Changes:

This PR adds documentation pages for the AlloyDBDocumentStore, AlloyDBEmbeddingRetriever, and AlloyDBKeywordRetriever.

How did you test it?

Notes for the reviewer

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have 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: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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Project	Deployment	Actions	Updated (UTC)
haystack-docs	Ready	Preview, Comment	May 15, 2026 2:53pm

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

[anakin87]

It's looking good.

I found an improvement opportunity.
In addition, please add the new retrievers to https://github.com/deepset-ai/haystack/blob/main/docs-website/docs/pipeline-components/retrievers.mdx#using-a-retriever

[anakin87]

Thank you!

Please also update https://github.com/deepset-ai/haystack/blob/main/docs-website/versioned_docs/version-2.29/pipeline-components/retrievers.mdx#using-a-retriever