Option to Hide Availability

[nzeager]

Is your feature request related to a problem? Please describe.
When a mentor signs up for a block of availability they don't know how many people will sign up. They may want to keep that schedule flexible, but limit the amount of time they spend mentoring. However if they delete availability then their sessions are cancelled.

Describe the solution you'd like
Under current availabilities we could have an option beside each availability to hide it so no one else can sign up for a session.

Describe alternatives you've considered
Currently, a mentor could request on the momentum-mentors-app channel that no one else sign up for them that day, but people might not be comfortable doing that and mentees may not see that.

[esparr]

@nzeager I am going to close this issue as the new availability endpoint will make it so they can cancel posted availabilities by 30 min intervals that have not been confirmed.