Allow both addition and removal of groups from expression policies

[Keyinator]

Describe the solution you'd like Allow expression policies to add and remove the current user from groups.

Describe alternatives you've considered None available to my knowledge.

Additional context Currently you can add a new users to groups using dynamic groups (https://goauthentik.io/docs/flow/stages/user_write#dynamic-groups). Sadly there's two missing features:

• You can't do it for existing users (Would love to update roles when users log in)
• You can't remove roles