Page for admins to add and delete PAT registration for Github groups

[jmgasper]

Note that we recently added functionality to have PAT records added for Github organisation invitations. See the new Organisations table.

To better support this functionality, and to make it easier for support to manage, we'd like to add a page that is ONLY FOR ADMINS so that admins can add and delete PAT records.

Admins should be able to add, delete PAT records for Github organisations. The PATs should not be displayed anywhere in the UI or returned from the backend API. They should be able to be added, but not edited. If the user wants to edit one, they'll need to delete the existing one and add a new one.

The PATs should be named and displayed in a table, with a button to add one that shows a form to fill out. Please use the password field type for the PAT itself, when adding.