feature: auto moderation

[Rapougnac]

Description

Add new discord's feature. Fixes #342

See:

• discord/discord-api-docs#4860
• discord/discord-api-docs#5090
• discord/discord-api-docs#5212
• discord/discord-api-docs#5242

Connected issues & other potential problems

-/-

Type of change

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [ ] Ran dart analyze or make analyze and fixed all issues
• [x] Ran dart format --set-exit-if-changed -l 160 ./lib or make format and fixed all issues
• [ ] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have checked my changes haven't lowered code coverage