Add support for groq

[svilupp]

• Added support for Groq, the fastest LLM provider out there. It's free for now, so you can try it out - you just need to set your GROQ_API_KEY. We've added Llama3 8b (alias "gllama3"), 70b (alias "gllama370") and Mixtral 8x7b (alias "gmixtral"). For the shortcut junkies, we also added a shorthand Llama3 8b = "gl3" (first two letters and the last digit), Llama3 70b = "gl70" (first two letters and the last two digits).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 92.90%. Comparing base (0873a8a) to head (c746606).

Files	Patch %	Lines
src/llm_openai.jl	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #139 +/- ## ========================================== - Coverage 92.98% 92.90% -0.09% ========================================== Files 42 42 Lines 3208 3212 +4 ========================================== + Hits 2983 2984 +1 - Misses 225 228 +3 ```

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