add index support

[imotai]

---

PR-Codex overview

This PR focuses on adding the ability to add indexes to existing collections in the document database.

Detailed summary

• Added AddIndexMutation message to the mutation protocol
• Added addIndex function to the doc_store.rs module
• Added addIndex function to the database_v2.ts module
• Added tests for the addIndex function in the client_v2.test.ts module

The following files were skipped due to too many changes: sdk/src/store/database_v2.ts, src/storage/src/db_store_v2.rs

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[codecov-commenter]

Codecov Report

Merging #573 (91e980a) into main (8c41779) will increase coverage by 0.60%.
The diff coverage is 84.61%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@            Coverage Diff             @@
##             main     #573      +/-   ##
==========================================
+ Coverage   63.97%   64.57%   +0.60%     
==========================================
  Files           9        9              
  Lines         433      446      +13     
  Branches       64       66       +2     
==========================================
+ Hits          277      288      +11     
- Misses        156      158       +2     

Flag	Coverage Δ
rust	64.57% <84.61%> (+0.60%)	⬆️

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

Impacted Files	Coverage Δ
sdk/src/account/db3_account.ts	62.50% <ø> (ø)
sdk/src/provider/storage_provider_v2.ts	76.92% <ø> (ø)
sdk/src/store/document_v2.ts	86.95% <ø> (ø)
sdk/src/store/database_v2.ts	81.92% <84.61%> (+0.49%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more