chore: update to OpenSearch 3.7.0

[marevol]

Summary

Update Fess to OpenSearch 3.7.0: bump the bundled OpenSearch plugins/modules and fix test expectations that broke with the new version.

Changes Made

• `plugin.xml`: opensearch-analysis-extension / analysis-fess / configsync / minhash 3.6.0 -> 3.7.0
• `module.xml`: `opensearch.version` 3.6.0 -> 3.7.0 (analysis-common, geo, lang-expression, lang-painless, mapper-extras, reindex, transport-netty4)
• `IndexingHelperTest`: removed `,"excludes":[]` from four expected `_source` JSON strings — OpenSearch 3.7.0 no longer serializes an empty `excludes` array in `FetchSourceContext`. Representation change only; query semantics are identical.

Testing

• `mvn antrun:run`: all 3.7.0 plugin/module zips download successfully from Maven Central and maven.codelibs.org.
• `mvn test -Dtest=IndexingHelperTest`: 25 tests, 0 failures.
• Full workspace build with tests passed against fess-parent with OpenSearch 3.7.0.

Breaking Changes

• None.

Additional Notes

• Depends on the fess-parent update (chore(deps): update OpenSearch to 3.7.0 and align dependencies fess-parent#53); merge that first.