Add filter-based deletion and string filter API to VectorStore

Add string-based filter deletion alongside the Filter.Expression-based deletion
for vector stores. This provides a more convenient API for simple filter cases
while maintaining the full flexibility of expression-based filtering.

Key changes:
- Add delete(Filter.Expression) and delete(String) methods to VectorStore
- Add default string filter implementation in VectorStore interface
- Implement filter deletion in Chroma/Elasticsearch/PgVector stores
- Add integration tests for both filter APIs across implementations

This extends vector store deletion capabilities while maintaining consistent
behavior across implementations.

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/vectordbs.adoc

@@ -27,12 +27,20 @@ Spring AI offers an abstracted API for interacting with vector databases through
 Here is the `VectorStore` interface definition:
 
 ```java
-public interface VectorStore {
+public interface VectorStore extends DocumentWriter {
+
+    default String getName() {
+		return this.getClass().getSimpleName();
+	}
 
     void add(List<Document> documents);
 
     Optional<Boolean> delete(List<String> idList);
 
+    void delete(Filter.Expression filterExpression);
+
+    default void delete(String filterExpression) { ... };
+
     List<Document> similaritySearch(String query);
 
     List<Document> similaritySearch(SearchRequest request);