Refactor role assignment methods

What does this MR do and why?

Refactor role assignment methods

Moving logic from EE::Member to Authz::Role. Separating the concerns here a little bit and trying to make member only responsible for knowing things like source, and what role a member has, and moving all the logic focused on member role and ability comparison to Authz::Role

part of: https://gitlab.com/gitlab-org/gitlab/-/issues/574071

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