feat: add opensearch provider

[n0ta26]

Closes #740

📑 Description

This draft PR introduces an OSS OpenSearch provider to Keep and validates it with a basic workflow against a local OpenSearch container.

Changes

• Implemented a new opensearch provider to integrate OSS OpenSearch with Keep.
• Added and started an OpenSearch container locally to validate the integration.
• Verified that the example workflow using the opensearch provider can successfully run end-to-end (query + index/document operations).

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

If the implementation looks good direction-wise, I would like to follow up with documentation updates.

Memo

• Added documentation for the OpenSearch provider and implemented a full index search example.
• Planning to add support for receiving alerts from OpenSearch in a future change.
• Planning to add branching logic for index creation and related operations in a future change (for now, the design is aligned with the OpenSearch Serverless provider).

[vercel]

@n0ta26 is attempting to deploy a commit to the KeepHQ Team on Vercel.

A member of the Team first needs to authorize it.

[CLAassistant]

All committers have signed the CLA.

[n0ta26]

I’ve updated the PR title.

[greptile-apps]

Skipped: This PR does not target one of your configured branches: (refactor/2512-nextjs-15)

[shahargl]

lgtm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 30.54%. Comparing base (97c263a) to head (fa8fb61).
⚠️ Report is 9 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (97c263a) and HEAD (fa8fb61). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (97c263a)	HEAD (fa8fb61)
	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5458       +/-   ##
===========================================
- Coverage   46.39%   30.54%   -15.86%     
===========================================
  Files         176      101       -75     
  Lines       18412    11669     -6743     
===========================================
- Hits         8543     3564     -4979     
+ Misses       9869     8105     -1764     

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[n0ta26]

@shahargl Thank you so much for reviewing this PR!
It was a really fun and valuable experience for me. 😊

I noticed there are a few alerts in GitHub Actions, but as far as I can tell they don’t seem to be caused by the changes in this PR.
I’m wondering if rebasing onto the latest main might change or resolve those alerts.

Could you please let me know what the next steps should be on my side?