[Feature] Save, load and set default for system prompt

[quazgar]

Feature description

I would like to store and reuse system prompts I commonly use, and also set one of these as default.

Use case or problem

Currently, I have to rewrite my favorite system prompt on every new chat. I would like to reuse other system prompts that were useful for me in the past.

Additional context

No response

Confirmation

• I have searched existing issues for this feature
• I have described why this feature would be helpful
• I am willing to help implement this feature (optional)