Fixes #21450 - Update rubocop to 0.51.0

Fixes #21026 - Clear cached notifications properly

Using `delete_all` for has_many does not trigger callbacks
on the associated objects, `dependent: :destroy` does.

Clearing the cache needs to happen anytime a notification
gets created, modified and destroyed, `after_commit`...

Fixes #17992, #18103 - Improve external usergroup errors

When one submit an user group with external user groups, and this
doesn't work for whatever reason, like:

Net::LDAP::Error - No route to host - connect(2)
LdapFluff::Generic::UnauthenticatedException...

fixes #21394 - user login with access token api

Fixes #21342 - fix core roles seeding

Core roles should always be up to date based on what's defined in seed
files. Users have no other way to update locked roles in newer Foreman
versions.

Fixes #21119 - set taxonomies in API

With this we correctly set the default taxonomy for non-admin users
in API calls. Admins are not touched at all, their context remains
"any context" for API calls. This also refactors various places
where tried to set the right taxonomy and combines them into single...

Fixes #18492 - add pf vertical navigation

Fixes #20541 - Include nested facts in CSV export

Fixes #12216 - support http proxies for compute resources

Fixes #21232 - verify IP sans when authenticating a SP