Added change_roles automod action

[metal0]

plugins:
  automod:
    config:
      rules:
        testrule:
          triggers:
            - match_words:
                words: ["testrl"]
          actions:
            change_roles:
              add: ["885116460261863425"]
              remove: ["885116523067375666"]

Fixes

This PR is meant to fix the issue of having both add_roles and remove_roles not functioning when used together.
I tried to fix the core issue at hand with the individual methods (i.e. the Member object's roles not being up-to-date by the time it reaches the 2nd action) but there was no super easy fix for this that I could find.

Regardless it would've still been 2 dapi requests, with this PR all role changes originating from a rule are now guaranteed to only be a single dapi request (since you can no longer use both add_roles and remove_roles)

@almeidx wtb review

[metal0]

WARNING!!!!

This will cause misconfiguration errors on bot startup (due to the config checks I added) if anyone has both add_roles AND remove_roles on their server's config!!

Flokie tried to add this to his instance and was instantly met with the misconfiguration error, do NOT merge this without some sort of migration

WARNING!!!!