qdrant: init package (#21146)

## Description

This PR introduces the new `langchain-qdrant` partner package, intending
to deprecate the community package.

## Changes

- Moved the Qdrant vector store implementation `/libs/partners/qdrant`
with integration tests.
- The conditional imports of the client library are now regular with
minor implementation improvements.
- Added a deprecation warning to
`langchain_community.vectorstores.qdrant.Qdrant`.
- Replaced references/imports from `langchain_community` with either
`langchain_core` or by moving the definitions to the `langchain_qdrant`
package itself.
- Updated the Qdrant vector store documentation to reflect the changes.

## Testing
- `QDRANT_URL` and
[`QDRANT_API_KEY`](583e36bf6b)
env values need to be set to [run integration
tests](d608c93d1f)
in the [cloud](https://cloud.qdrant.tech).
- If a Qdrant instance is running at `http://localhost:6333`, the
integration tests will use it too.
- By default, tests use an
[`in-memory`](https://github.com/qdrant/qdrant-client?tab=readme-ov-file#local-mode)
instance(Not comprehensive).

---------

Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Erick Friis <erickfriis@gmail.com>

libs/partners/qdrant/tests/integration_tests/conftest.py

@@ -0,0 +1,15 @@
+import os
+
+from qdrant_client import QdrantClient
+
+from tests.integration_tests.fixtures import qdrant_locations
+
+
+def pytest_sessionfinish() -> None:
+    """Clean up all collections after the test session."""
+    for location in qdrant_locations():
+        client = QdrantClient(location=location, api_key=os.getenv("QDRANT_API_KEY"))
+        collections = client.get_collections().collections
+
+        for collection in collections:
+            client.delete_collection(collection.name)