user-profile: add authorised-users field

[oliver-sanders]

Add a new field called "authorized users" (or similar) to the user-profile containing all users listed in the user's authentication config when running in multi-user mode.

This field will be used by the Cylc UI to allow quick access to the listed UI Servers via a user-name dropdown/filter box in the top-left of the UI.

Example:

   c.CylcUIServer.user_authorization = {
       "user1": ["read", "pause", "play"],
        "group:group1": ["read"],
   }

In multi-user mode (when the application class is CylcHubApp):

user_profile = {
    'kind': 'user',
    'name': 'me',
    'authorized users': ['user1'],

In single user mode:

user_profile = {
    'kind': 'user',
    'name': 'me',
    'authorized users': [],

Note, we don't need to check that the listed users are authorised, if they are not that will become obvious when the user tries to access their UIS.

Pull requests welcome!