Check to see whether the current user is an admin of the open repo

[lostintangent]

Currently, we don't check if the user is an admin on the current repo or not. We simply check to see if they can access alerts via the API, and use that to determine if we can show them in the tree. That said, if the user isn't an admin, then we shouldn't even display the options for enabling dependabot and/or learning more about code scanning.

Repo committers can currently see code scanning alerts, but not dependabot alerts. The later will change in the near future.