Implement Python `Enum` class on `RealmRole` to allow exhaustive match checks

[touilleMan]

e.g.

parsec-cloud/server/parsec/components/memory/vlob.py

Lines 256 to 265 in 74a5427

	match realm.get_current_role_for(author_user_id):
	case RealmRole.READER | None:
	return VlobUpdateBadOutcome.AUTHOR_NOT_ALLOWED
	case RealmRole.OWNER | RealmRole.MANAGER | RealmRole.CONTRIBUTOR:
	pass
	case unknown:
	# TODO: Implement `Enum` on `RealmRole` so we can use `assert_never` here
	assert False, unknown