How Much Notice Should Mentors Have for New Meeting

[nzeager]

Is your feature request related to a problem? Please describe.
Mentors may prefer some notice that they'll have a meeting on their schedule. Currently mentees can sign up just a few minutes before a meeting would begin.

Describe the solution you'd like
Somewhere near the Notifications section it might be helpful to have a Settings section where it could say 'Mentees can must sign up at least _ hours in advance of a meeting.' There could be a pulldown with 0-5, or however high we want to go. There could even be a 24 option if some people want a full day's notice.

Then when a mentee goes to sign up a times, we wouldn't display availability that is sooner than the mentor has set.

Describe alternatives you've considered
We could just pick a standard amount of time for everyone, like 1 hr, and filter the signup times the same way for all mentors.

We could have a section in the mentor's profile where they can describe their preferences, which we'd display on the signup page, and trust students to follow their instructions.

[esparr]

This should be linked with this back end issue: https://github.com/orgs/TeamProductionSystem/projects/2/views/1?pane=issue&itemId=44520684