Update user_group_member_roles when SAML/LDAP users are synced and when memberships are activated

What does this MR do and why?

This MR introduces Authz::UserGroupMemberRoles::UpdateForGroupMemberService to centralize the logic when a group membership is created/updated.

We then simply call update_user_group_member_roles on a Member instance (executes the new service) in the following scenarios:

1. When a group member is activated
2. When members are created during SAML group link synchronization
3. When members are created during LDAP group link synchronization

References

Implements the following:

1. Create user_group_member_roles when SAML/LDAP/e... (#553339 - closed)
2. Update user_group_member_roles when a member is... (#521131 - closed)

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