[ai] fine tune our Gemini Code Assist review config

[pq]

Specifically:

• fill in ignore_patterns (avoid noise and save tokens)
• add more opinions to the styleguide (discouraging use of deprecated, experimental code, ...)
  • (🔎 Consider https://github.com/JetBrains/junie-guidelines for inspiration)