Add AlloyDB vector writer.

[claudevdm]

Disabled test while I figure out how to configure the database arguments to run in dataflow and github action runners.

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• Mention the appropriate issue in your description (for example: addresses #123), if applicable. This will automatically add a link to the pull request in the issue. If you would like the issue to automatically close on merging the pull request, comment fixes #<ISSUE NUMBER> instead.
• Update CHANGES.md with noteworthy changes.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

See the Contributor Guide for more tips on how to make review process smoother.

To check the build health, please visit https://github.com/apache/beam/blob/master/.test-infra/BUILD_STATUS.md

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI or the workflows README to see a list of phrases to trigger workflows.

[claudevdm]

R: @damccorm

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control. If you'd like to restart, comment assign set of reviewers

[damccorm]

Is there a set of supported types here? Is it basically anything that Alloy supports/is there a doc we could link to?

[claudevdm]

I think the supported types are anything that RowCoder can handle, I added this to the docstring.

[codecov]

Codecov Report

Attention: Patch coverage is 51.06383% with 69 lines in your changes missing coverage. Please review.

Project coverage is 59.48%. Comparing base (949b988) to head (040dc47).
Report is 83 commits behind head on master.

Files with missing lines	Patch %	Lines
...dks/python/apache_beam/ml/rag/ingestion/alloydb.py	51.06%	69 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #33841      +/-   ##
============================================
- Coverage     59.48%   59.48%   -0.01%     
  Complexity     4683     4683              
============================================
  Files          1348     1349       +1     
  Lines        184681   184902     +221     
  Branches       4455     4455              
============================================
+ Hits         109852   109981     +129     
- Misses        71088    71180      +92     
  Partials       3741     3741              

Flag	Coverage Δ
python	81.17% <51.06%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.