Add missing guild incident fields

[Soheab]

Summary

These new fields were added to the docs PR:

• dm_spam_detected_at
• raid_detected_at

I'm not sure if the ..._detected methods are necessary...

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[Rapptz]

This seems mostly fine, but minor bikeshedding nit: methods checking for boolean stuff tend to have the is_ prefix, e.g. is_timed_out() or is_on_mobile, etc.