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## What this PR does
### Release note
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```release-note
[feature] add ferretdb tests
```
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## Summary by CodeRabbit
- Tests
- Added an end-to-end test that provisions a FerretDB instance on
Kubernetes, waits for readiness and init completion, verifies
connectivity to read/write Postgres services (including endpoint
convergence), accounts for known RO delays, and performs full cleanup.
Uses timeouts and retries for stability.
- Chores
- No user-facing product changes.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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