Improve: explain what how log drain works

[hequ]

What part of the documentation needs improvement?
Drain logs: https://github.com/coollabsio/coolify-docs/blob/v4.x/docs/knowledge-base/drain-logs.md

Describe the enhancement you'd like to see:
Explain what log drain actually does, so users can reason the effects of applying this setting. Explain that when you enable the "Drain logs" option in your application settings, it changes the container logging configuration and starts sending the log events to fluentbit log drain container on port 24224 if the log drain container is running. And you can start that log drain container by enabling the custom fluentbit configuration or any of the pre-configured log drain options.

Also explain that if you configure custom fluentbit settings, you need fluentbit input that is listening on port 24224 like this:

[INPUT]
    Name         forward
    Listen       0.0.0.0
    Port         24224
    Tag          docker

Why do you think this enhancement is valuable?
If you are not familiar how log forwarding works, this can be really tricky to set up. I think currently this is especially tricky because the coolify UI just has these "enable log drain" buttons on both server and application, but when you enable those and you don't see any logs, it is a frustrating experience. I think the main point in this is that you must understand how fluentbit reads the logs and how you can connect docker to send it logs to fluentbit.