mgr/dashboard: Add support for "always_on_modules"
Some modules are always enabled, for example, the "pg_autoscaler":
The full list of "always_on_modules" is available here:
Ceph Dashboard should be aware of these modules to correctly display if the module is enabled and to prevent the user from disabling it.
For example, the "progress" module is always enabled, but Ceph Dashboard shows it as "Disabled":