[litellm] Add UI validation in AI settings

[dlqqq]

Problem

As described in title.

Proposed Solution

We should check the following:

• Show a warning if a user inputs a model ID is not listed in the suggestions. This doesn't mean that the model will fail, it just means that it may fail.

• Show a warning if the new model lacks authentication.

• Show a warning if an optional dependency is required for use. I think this only happens for bedrock/ models, which require boto3.

Notes

This is probably the last issue to work on, since we need to add API keys input & model parameters input first.