feat(connectors): add Meilisearch sink connector

[countradooku]

Summary

• add the Meilisearch sink connector using the official meilisearch-sdk
• document the sink configuration and payload mapping behavior
• add Docker-backed integration coverage for indexing JSON messages into Meilisearch

Motivation

This splits the sink portion out of #3404 so the Meilisearch sink can be reviewed and merged independently from the source connector.

Closes #3495.

Validation

• cargo sort --no-format --workspace
• cargo test -p iggy_connector_meilisearch_sink
• cargo clippy -p iggy_connector_meilisearch_sink --all-targets -- -D warnings
• env CARGO_BIN_EXE_iggy-server=... CARGO_BIN_EXE_iggy-connectors=... cargo test -p integration --test mod -- connectors::meilisearch::meilisearch_sink
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 78.12500% with 154 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.41%. Comparing base (4a48008) to head (3a80598).

Files with missing lines	Patch %	Lines
core/connectors/sinks/meilisearch_sink/src/lib.rs	78.12%	137 Missing and 17 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3497       +/-   ##
=============================================
- Coverage     74.27%   45.41%   -28.86%     
  Complexity      937      937               
=============================================
  Files          1259     1257        -2     
  Lines        125969   110618    -15351     
  Branches     101644    86335    -15309     
=============================================
- Hits          93558    50239    -43319     
- Misses        29396    57664    +28268     
+ Partials       3015     2715      -300     

Components	Coverage Δ
Rust Core	37.94% <78.12%> (-37.22%)	⬇️
Java SDK	58.57% <ø> (ø)
C# SDK	71.40% <ø> (-0.71%)	⬇️
Python SDK	88.88% <ø> (ø)
PHP SDK	84.29% <ø> (ø)
Node SDK	91.13% <ø> (-0.10%)	⬇️
Go SDK	40.36% <ø> (ø)

Files with missing lines	Coverage Δ
core/connectors/sinks/meilisearch_sink/src/lib.rs	78.12% <78.12%> (ø)

... and 375 files with indirect coverage changes

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[ryerraguntla]

overall correct approach - JSON-object document model with generated PK is sound, wait_for_tasks + partial-error accounting is thoughtful. test coverage is present but there is
coverage gap — only happy-path (2 JSON messages indexed, iggy_id present). No test for: document_action = update semantics, include_metadata = false, raw-payload base64 fallback, or wait_for_tasks = false fire-and-forget path. Not a merge-blocker given this is the initial connector, but tracking it. Along with coverage, please take care of the above mentioned issues.

[ryerraguntla]

/author

[countradooku]

/ready

[countradooku]

/ready

[ryerraguntla]

@countradooku - few blockers, many nits. One thing which is encouraged is to have more test coverage. - Integration coverage: no tests for Payload::Raw, Payload::Text, wait_for_tasks=false, custom primary_key, create_index_if_not_exists=false error path. (intro)

[ryerraguntla]

/author

[countradooku]

/ready