Added Groq as an provider

[Penagwin]

Adds support for Groq.com

Addresses #427

The logo is a little janky, and heads up that they keep changing their rate limits.
Currently it's

The rate limit is set to 20 requests per minute and 20 requests per 10 minutes, operating simultaneously. Whichever limit is reached first triggers the rate limit:

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Name	Status	Preview	Updated (UTC)
big-agi-open	✅ Ready (Inspect)	Visit Preview	Mar 1, 2024 6:25pm

[enricoros]

Nice! From a quick read it seems you hit all the places to modify to add support - good job.
Will need my laptop to test and merge, will do that soon.

[Penagwin]

I discovered Groq does support fetching the models although it's not documented.

So I added support for that

[enricoros]

Thanks @Penagwin - great quality contribution. Reviewed and updated the icon.
Groq is really fast, I can consider new use cases with it.
Also good job to find the undocumented model list endpoint - very useful as it reduced ongoing maintenance cost, and shows models as soon as they're released!