Per user profile choices for resource allocation

[felder]

When discussing issue #2330 with @yuvipanda I asked if it would be possible to allow people with special high resource use cases (16GB of RAM in this case) the option of choosing between resource allocations on sign in. The idea being to default to typical resource allocations while allowing a user to select higher ones when they know they are going to performing tasks which require them.

He pointed me to: https://zero-to-jupyterhub.readthedocs.io/en/latest/jupyterhub/customizing/user-environment.html#using-multiple-profiles-to-let-users-select-their-environment

This might be a good solution to allow us to keep costs down by providing additional resources on demand (as opposed to all the time).

In fact, maybe we could do that for students in classes which have requested higher resource allocations as well.