docs: Improve documentation on syncing UserProfile bool flags via ldap.
docs: Improve documentation on syncing UserProfile bool flags via ldap.

It's better to explicitly list the possibilities. Also, the
recommendation regarding is_active should be changed to a strict
"Don't", as Subscription.is_user_active is a denormalized field and
flipping a user's is_active will cause inconsistent state by leaving
Subscriptions unupdated. Given that similar things can be introduced in
the future for any other flag not officially supported by having a
setter, the recommendation should "Don't" in general.

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