Turn off moderation if omni-moderation-latest is not available

Problem/Motivation

When working with a company account in OpenAI, there is the possibility to only allow certain models. This means that you can turn off the moderation models. This is very bad practice since the accounts can get banned, but we have one reported instance of such an account.

We need the OpenAI model to still work in these instances and people might not know that we do the opinionated thing of turning on moderation by default.

We need to inform when this happens.

Proposed resolution

When the user saves the OpenAI Settings form, we look so that omni-moderation-latest is available. If its available, nothing happens.
If moderation is enabled, we set an error message with the information that they either need to manually run a drush command to turn off moderation, but that it can have sever consequences, or that they have to ask their administrator to give them access to omni-moderation-latest.