Test LLM service on create

[SmittieC]

When a user adds a new LLM service to their team, it could be useful if we allow them to quickly test the integration (we can either do it autmatically in the background or allow them to enter some text to test it). This will reveal any issues with the integration there and then. If we don't do this, the first failure will happen when someone chat with the bot, but the error will be masked, since we show some generic error message to the user (or just tell them something went wrong if they use an external channel).