feat(vector-db): add support for Pinecone client

Adds Pinecone as a supported vector database option.

- Implements `PineconeClient` with support for common operations: `add`, `query`, `delete`, `reset`.
- Emulates namespace support using metadata filtering (`collection_name` prefix).
- Dynamically configures Pinecone via the following env vars:
  - `PINECONE_API_KEY`
  - `PINECONE_ENVIRONMENT`
  - `PINECONE_INDEX_NAME`
  - `PINECONE_DIMENSION`
  - `PINECONE_METRIC`
  - `PINECONE_CLOUD`
- Integrates cleanly with the vector DB abstraction layer.
- Includes markdown documentation under `docs/getting-started/env-configuration.md`.

BREAKING CHANGE: None

backend/open_webui/retrieval/vector/connector.py

@@ -20,6 +20,10 @@ elif VECTOR_DB == "elasticsearch":
     from open_webui.retrieval.vector.dbs.elasticsearch import ElasticsearchClient
 
     VECTOR_DB_CLIENT = ElasticsearchClient()
+elif VECTOR_DB == "pinecone":
+    from open_webui.retrieval.vector.dbs.pinecone import PineconeClient
+
+    VECTOR_DB_CLIENT = PineconeClient()
 else:
     from open_webui.retrieval.vector.dbs.chroma import ChromaClient