partners: add Elasticsearch package (#17467)

### Description
This PR moves the Elasticsearch classes to a partners package.

Note that we will not move (and later remove) `ElasticKnnSearch`. It
were previously deprecated.
`ElasticVectorSearch` is going to stay in the community package since it
is used quite a lot still.

Also note that I left the `ElasticsearchTranslator` for self query
untouched because it resides in main `langchain` package.

### Dependencies
There will be another PR that updates the notebooks (potentially pulling
them into the partners package) and templates and removes the classes
from the community package, see
https://github.com/langchain-ai/langchain/pull/17468

#### Open question
How to make the transition smooth for users? Do we move the import
aliases and require people to install `langchain-elasticsearch`? Or do
we remove the import aliases from the `langchain` package all together?
What has worked well for other partner packages?

---------

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

cookbook/self_query_hotel_search.ipynb

@@ -1083,7 +1083,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from langchain_community.vectorstores import ElasticsearchStore\n",
+    "from langchain_elasticsearch import ElasticsearchStore\n",
     "from langchain_openai import OpenAIEmbeddings\n",
     "\n",
     "embeddings = OpenAIEmbeddings()"