Better client UX when self-scheduling is disabled

Improve UX for client self-schedule when clinician has not made it available.

When a clinician has not enabled client self-scheduling, clients who try to schedule see "Scheduling unavailable. To schedule a session, please reach out to your provider directly." Instead of a dead end, the screen should offer an option right there to send a message to the provider, or better, hide the schedule button entirely when the feature is turned off. The current message makes the feature seem broken, which is a poor user experience.