Add Ban User functionality

[Demigodrick]

Adds the ability for an admin to ban a user from the instance.

[db0]

Thanks. Is this tested?

[Demigodrick]

Yes, have tested it live and worked with no issues.

From the modlog - for the ban, time is unix time when the ban should expire. Not from the point of making the ban (hence the expired 54 years ago).

Now i think about it, is it worth adding that into the code?

[db0]

The best actually would be to have the user pass a datetime object and convert it to the lemmy int on our end

[db0]

I'll send a patch in a bit