docs retriever improvements (#4430)

# Docs: improvements in the `retrievers/examples/` notebooks

Its primary purpose is to make the Jupyter notebook examples
**consistent** and more suitable for first-time viewers.
- add links to the integration source (if applicable) with a short
description of this source;
- removed `_retriever` suffix from the file names (where it existed) for
consistency;
- removed ` retriever` from the notebook title (where it existed) for
consistency;
- added code to install necessary Python package(s);
- added code to set up the necessary API Key.
- very small fixes in notebooks from other folders (for consistency):
  - docs/modules/indexes/vectorstores/examples/elasticsearch.ipynb
  - docs/modules/indexes/vectorstores/examples/pinecone.ipynb
  - docs/modules/models/llms/integrations/cohere.ipynb
- fixed misspelling in langchain/retrievers/time_weighted_retriever.py
comment (sorry, about this change in a .py file )

## Who can review
@dev2049

docs/modules/indexes/vectorstores/examples/elasticsearch.ipynb

@@ -7,7 +7,7 @@
    "source": [
     "# ElasticSearch\n",
     "\n",
-    "[Elasticsearch](https://www.elastic.co/elasticsearch/) is a distributed, RESTful search and analytics engine. It provides a distributed, multitenant-capable full-text search engine with an HTTP web interface and schema-free JSON documents.\n",
+    ">[Elasticsearch](https://www.elastic.co/elasticsearch/) is a distributed, RESTful search and analytics engine. It provides a distributed, multitenant-capable full-text search engine with an HTTP web interface and schema-free JSON documents.\n",
     "\n",
     "This notebook shows how to use functionality related to the `Elasticsearch` database."
    ]