🐳 : Further Docker build Cleanup & Docs Update (#1502)

* refactor: post-cleanup changes:
- add more unnecessary paths to .dockerignore
- remove librechat.yaml from main compose file (prevents from being required)
- do not create librechat.yaml during build (does nothing)

* docs: make config file instructions easier to read, more info throughout other docs

* docs: add custom config to menu

* Update custom_config.md

* Update docker_compose_install.md

docs/install/configuration/ai_setup.md

@@ -48,6 +48,8 @@ Using the default environment values from [/.env.example](https://github.com/dan
 
 This guide will walk you through setting up each Endpoint as needed.
 
+For **custom endpoint** configuration, such as adding [Mistral AI](https://docs.mistral.ai/platform/client/) or [Openrouter](https://openrouter.ai/) refer to the **[librechat.yaml configuration guide](./custom_config.md)**.
+
 **Reminder: If you use docker, you should [rebuild the docker image (here's how)](dotenv.md) each time you update your credentials**
 
 *Note: Configuring pre-made Endpoint/model/conversation settings as singular options for your users is a planned feature. See the related discussion here: [System-wide custom model settings (lightweight GPTs) #1291](https://github.com/danny-avila/LibreChat/discussions/1291)*