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`](https://github.com/langchain-ai/langchain/pull/21146/commits/583e36bf6bb38d7d2495499aae75a1912013ce76)
env values need to be set to [run integration
tests](https://github.com/langchain-ai/langchain/pull/21146/commits/d608c93d1fea7d2d84dda431caf42d2f3c7588db)
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).

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Co-authored-by: Erick Friis <[email protected]>
Co-authored-by: Erick Friis <[email protected]>