refactor: improve handling of permissions, users, and settings

[b-rowan]

This PR aims to:

• Move user handling into the database
• Refactor permission handling into a more strict style
• Add a settings page for working with locally managed users, including adding and removing them and modifying their permissions
• Allow parsing a "top level" permission structure into a menu of user-configurable permissions, to allow the user permissions to be configured via the UI
• Add an API endpoint to allow users to be configured programmatically
• Allow enabling and disabling users so that the initial user created by goosebit can be disabled if needed

[b-rowan]

Fixes: #276

[b-rowan]

@tsagadar RE #276, this is pretty much my proposed solution to that, in theory we could actually handle API path permissions too (have BFF use UI permissions and separate API permissions), but I think just being able to properly configure users is good enough. In any case, even with API permissions, the program could just use the BFF endpoints anyway.

This feels like a relatively elegant solution that allows getting rid of some configuration inside the initial yaml file, let me know your thoughts.

[tsagadar]

Few things that popped out from the code. Will do some manual testing at a later stage.

[tsagadar]

Tried out the new functionality. Looks nice, but I had a few issues to use it. Some of them likely can be addressed in a later PR as well.

1. Initial user creation page: best to add a short explanation like "Welcome to goosebit. As a first step create your admin account."
2. Users without the "goosebit.devices" permission cannot use the UI: after log-in one is redirected to /ui/devices and if permissions are mission it just shows {"detail":"Not enough permissions"}. Once in that state, even logout is not possible. So one should get redirected to the first screen where read permissions are given.
3. Changing user permissions is not yet implemented
4. Creating a user without permission is possible but does make no sense. Disallow it?
5. Likely an old issue: login in with wrong password does not show any error

[tsagadar]

See #278 (comment) for open issues.

[b-rowan]

Changing user permissions is not yet implemented

Do we want to be able to reset a user's password via the Update User UI? Can add that as well while doing this if its a feature we want.

[b-rowan]

@tsagadar Fixed issue 1, 2 and 4, will do 3 alongside user password resets if you feel we want that feature, and not entirely sure whats going on with 5.

[tsagadar]

Just a few minor things to address.

There will be a need that user can be modified (permissions and password) by "admins". But I would not add it to this PR.