Allow configuration of MAX_TOKEN_OUTPUT_LENGTH for custom models

[ai-made-approachable]

At the moment adding custom models is a real hassle, as you need to find out that you need to map your custom model to one of the existing models in this file here:

chatbot-ui/lib/chat-setting-limits.ts

Line 63 in 3cfb3f3

MAX_TOKEN_OUTPUT_LENGTH: 4096,

Otherwise you get a MAX_TOKEN_OUTPUT_LENGTH error.

I think this field should be configurable in the custom model settings, to prevent that issue.