Add user activity checker

[VanillaSixtySix]

Add a moderator-only command to provide the initiator with information on whether a user is considered active in the server or not.

These values are not expected to change, so it's fine to hardcode.

Active criteria:

• The user's first join was over 3 months ago and sent 2000 messages in the last 3 months.
• The user's first join was between 2 weeks and 3 months ago and sent 500 messages.
• The user's first join was less than 2 weeks ago.
• The user has a set "always active" role.

[CloudburstSys]

Can get the first join by using Discord Search API and getting the first message mentioning them in the welcome channel

Active criteria checking: > 3 months - Use Discord Search API to get last messages after 3 months ago. > 2 weeks but < 3 months - Use Discord Search API to get total message count. < 2 weeks - True role - has a role in a "always active" role list