feat(coral): Enable superadmin to access coral

# Description

User with role SUPERADMIN should be able to access Coral. The change will be done in multiple steps behind a feature flag.

## Changes needed

Note: This is a in-between solution. We want to have routing and views based on a more fine-grained permission model. Implemenations should be made in a way that they are easy to do / remove / changed to permissions later.

## FE
- [x] Show superadmin specific navigation (#2303)
- [x] update routing based on userrole (#2303)
- [x] remove the top level nav quick action links for superadmins (https://github.com/Aiven-Open/klaw/pull/2426)
- [ ] remove feature flag
- [ ] Add "coral interface available" preview banner in Klaw for superadmins

## BE
- add navigation guards to make sure superadmins can't do any actions they shouldn't be able to do and get good error messages about it