GPT4 support

[webbertakken]

Context

GPT4 has reached general availability on july 6th, 2023. It also states that the limits will become higher.

Suggested solution

Use GPT4 exclusively, with a fallback to GPT-3.5-Turbo in case of no availability.

Considered alternatives

• Immediately switching to our own fine-tuned model (probably too early)
• Staying at GPT-3.5-Turbo (viable, but let's see if we can make GPT4 do some work for us)

Additional details

Perhaps we need to look into and SDK that can more easily set the context and help us finetune our prompts and store context between requests.