[ci][integrations] Enable Elasticsearch vector-store tests

[kaiwangleo]

Fixes #999

Root cause

Filtered queryEmbedding requests applied the combined filter through SearchRequest.postFilter(...) after Elasticsearch had already selected the unfiltered KNN top-k results. This could return fewer than k matching documents.

Fix

Apply the combined filter directly to the Elasticsearch KNN clause through KnnSearch.Builder.filter(...).

Existing unified filters, raw filter_query handling, AND composition, k, num_candidates, and exception behavior are preserved.

Tests

• WSL Maven compilation for the Elasticsearch module passed.
• Real Elasticsearch 8.19 integration tests passed: 6 tests, 0 failures, 0 errors, 0 skipped.
• Regression coverage includes:
  • unified filters;
  • raw filter_query;
  • combined filters;
  • matching documents outside the unfiltered top-k.

[wenjin272]

Thanks for taking this on. I have adjusted the PR title to reflect the current CI-focused scope.