Resolve "Allow adjusting the subdomains applications run on"

Closes #1283 (closed)

To do:

1. Add a job that creates a configmap that contains the default domain an application runs on
   • This configmap can be adjusted by the users. Because the CM is created by a job (that never overwrites existing CMs), Flux won't revert the changes users make.
2. Use the domain from the CM in all applications' oauth2 client
3. Use the domain from the CM in all applications' helm values
4. Create issues for the Dashboard to use this variable as well. dashboard#75 (closed)