Removing models does not alert experiments

[bderenzi]

Right now the model used is determined by the llm string and the llm_provider_id. If we change the available llm models (e.g., because a provider is deprecating old models), the experiment is never alerted / there is no check.

Possible solutions:

• When we edit a provider we could check the old set of models against the new and for any that have been removed we could generate an error / warning to go and update the experiment to first remove dependency on the model that is getting removed.

That solution is a little annoying for the user unless in the same edit-provider UI we allow them to select a replacement. For example, imagine the case where we're removing llama-3 and adding llama-3.1. The steps would be:

1. Edit the provider to remove llama-3 and add llama-3.1
2. Get an error that projects X, Y, Z are all reliant on llama-3 so we can't remove them yet
3. Change the edit to just add llama-3.1
4. Go manually update all projects relying on the old model
5. Return to the edit provider screen to remove llama-3

An alternative:

1. Edit the provider to remove llama-3 and add llama-3.1
2. Get an error that projects X, Y, Z are all reliant on llama-3 so we can't remove them yet. Ask for a replacement model that will be applied to all experiments that are affected
3. Confirm replacement and be done.

[SmittieC]

Option 2 is deffs better UX. +1 for that