RFE: implement Integration Domain UnitTests with Mock

[f-trivino]

The view integration domain unit tests end calling the corresponding POST request for domain enrollment. We don't really want to enroll with an integration domain as we will need to add more infra to the GitHub Actions (e.g. IPA/LDAP/ADDC servers)...

This RFE is all about to implement mocks for the app REST-API calls, a JSON should be returned instead of enrolling with a domain.