secured routes for adding allow/denylist

[alexandermichels]

This depends on #127, but the idea would be to create secured routes (not using the JupyterHub auth) for adding users to the allowlist/denylist solution. The solution should have all of the parameters in the URL so that we can provide HPC facilitators with simple links to approve/deny.

An initial thought would be to generate a random string that we match against in the request to secure it. I'm imagining we format the route such that we can send HPC admins a link like:

[Compute server]/v2/:userId/add-allow?hpc=[HPC_RESOURCE]&key=[RANDOMLY_GENERATED STRING]

Open to better solutions though