feat: Jan implements preset configurations for popular models

[eckartal]

Problem
Users currently lack preset configurations for popular models like Llama-3-8b-Instruct, which results in manual setup that can be error-prone and intimidating for non-expert users. Plus, the "Model Parameters" section does not offer enough flexibility for configuring different models.

Success Criteria

• Introduce preset configurations for commonly used models to simplify setup for users.
• Improve the "Model Parameters" section to allow for more flexible configurations that can be easily adapted to support various models without manual intervention.

Additional context
Detailed feedback: https://www.reddit.com/r/LocalLLaMA/comments/1cclmjk/comment/l1byjva/?context=3