feat: Azure Cognitive Search Plugin (#815)

* feat(AzureCognitiveSearchPlugin)

* feat(tools/AzureCognitiveSearch.js): Add a new plugin (not structured
  version)
* feat(tools/structured/AzureCognitiveSearch.js): Add a new plugin (structured version)
* feat(tools/manifest.json, tools/index.js, tools/util/handleTools.js):
  Add configurations for the plugin
* feat(api/package.json, package-lock.json): Installed a new package for the
  plugin (@azure/search-documents)
* feat(.env.example): Add new environment variables for the plugin

Here is the link to the corresponding discussion page:
https://github.com/danny-avila/LibreChat/discussions/567

* docs(AzureCognitiveSearchPlugin)

* docs(features/plugins/azure_cognitive_search.md): Add a new document
  for the plugin

* (fix:.env.example)

* reverted extra whitespaces removed by the editor

* docs(mkdocs.yml)

* Add the Azure Cognitive Search Plugin's documentation item to
mkdocs.yml.

api/package.json

@@ -21,6 +21,7 @@
   "homepage": "https://github.com/danny-avila/LibreChat#readme",
   "dependencies": {
     "@anthropic-ai/sdk": "^0.5.4",
+    "@azure/search-documents": "^11.3.2",
     "@dqbd/tiktoken": "^1.0.2",
     "@fortaine/fetch-event-source": "^3.0.6",
     "@keyv/mongo": "^2.1.8",