Encourage Mentees to Sign Up with New Mentors

[nzeager]

Is your feature request related to a problem? Please describe.
Mentees will often default to mentors they have already worked with. New mentors frequently post time and don't get any session requests.

Describe the solution you'd like
We could somehow set up the session signup page in a way that encourages users to consider mentors the haven't worked with. We could display mentors in order of least sessions they've worked with together to most. Or we could have a section with mentors they haven't worked with, asking users to consider signing up with one of them.

Describe alternatives you've considered
We could talk with current students and ask them to work with different mentors. If we have a mentee's getting started page on the documentation we could ask them to vary the mentors they work with.

Additional context
We could alternatively use the ordering of mentors to emphasize mentors that have fewer sessions scheduled, so no mentor gets overwhelmed with sessions.