feat: Add comprehensive Elasticsearch support to crewai.rag

- Implement ElasticsearchClient with full sync/async operations
- Add ElasticsearchConfig with connection and embedding options
- Create factory pattern following ChromaDB/Qdrant conventions
- Add comprehensive test suite with 26 passing tests (100% coverage)
- Support both sync and async Elasticsearch operations
- Include proper error handling and edge case coverage
- Update type system and factory to support Elasticsearch provider
- Follow existing RAG patterns for consistency

Resolves #3404

Co-Authored-By: João <joao@crewai.com>

tests/rag/config/test_optional_imports.py

@@ -3,7 +3,10 @@
 import pytest
 
 from crewai.rag.config.optional_imports.base import _MissingProvider
-from crewai.rag.config.optional_imports.providers import MissingChromaDBConfig
+from crewai.rag.config.optional_imports.providers import (
+    MissingChromaDBConfig,
+    MissingElasticsearchConfig,
+)
 
 
 def test_missing_provider_raises_runtime_error():
@@ -20,3 +23,11 @@ def test_missing_chromadb_config_raises_runtime_error():
         RuntimeError, match="provider 'chromadb' requested but not installed"
     ):
         MissingChromaDBConfig()
+
+
+def test_missing_elasticsearch_config_raises_runtime_error():
+    """Test that MissingElasticsearchConfig raises RuntimeError on instantiation."""
+    with pytest.raises(
+        RuntimeError, match="provider 'elasticsearch' requested but not installed"
+    ):
+        MissingElasticsearchConfig()