[V3 Warnings] changes to the warnings cog

[palmtree5]

Type

• Bugfix
• Enhancement
• New feature

Description of the changes

See #1851
The goal of this is to implement the main suggestions there. Still need to confirm whether the two Sentry issues linked are still occurring with these changes.

Summary:

• The text shown when entering action commands has been clarified with some formatting.
• Adding a command is no longer a all-or-nothing type deal (so you can have both have commands, one or the other, or none)
• Now sends a message to the warned user indicating they've received a warning and in what server
• Users with permissions to run warn/unwarn cannot add/remove warnings from themselves