Add default prompt for LLM

[RichDom2185]

Description

Partially supersedes #2554 together with #2657.

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update
• [ ] Code quality improvements

Checklist

• [ ] I have tested this code
• [ ] I have updated the documentation