docs(ai): trim external container docs

[rickstaa]

This pull request makes the external container docs more concise.

[ad-astra-video]

Most of the updates look fine. Couple things to look at:

• The capacity field updated explanation is incorrect. Setting warm: true doesn't make it fast :). Need to ensure loading of the model in the auto-scaling setup is fast!
• Looks like the reference to (including error codes) was removed in the explanation of the container management acting as a pass through. My only concern is if the container management system returns an error that is not a known error for the pipeline it can return "normal" response in go-livepeer right? or did we fix that?