SOA RNAME is not validated and can have invalid values

[peteeckel]

Versions
NetBox Version: 3.6.1
NetBox DNS Version: 0.18.10
Python Version: 3.8.13

Describe the bug
Although the SOA RNAME field for a zone represents an E-Mail address, it needs to be represented in the SOA field as an FQDN, i.e. with the @ substituted by a ..

Currently NetBox DNS does not enforce this, and it also doesn't check for FQDN when the field is validated at all. This may lead to invalid SOA records being created for the zone.

To Reproduce
Steps to reproduce the behavior:

1. Create or edit a zone
2. Set the 'Responsible' field to [email protected]
3. Save the zone

Expected result
An error message indicating that the RNAME is not an FQDN is created.

Actual result
The setting is accepted and the SOA record for the zone contains [email protected] in the RNAME field.