Description of problem:
Make it possible to choose Primary interface identifier in Global Registration Template. We already have this feature for REX interface.

Why this is needed:

When a host has multiple NICs, Satellite will choose the first one from the list as primary interface during registration. For example when ens7, ens8, ens9 are present, Satellite will choose ens7 as primary and there's currently no way to change this behavior.

If the interface Satellite had chosen as primary isn't a part of subnet associated with the hostgroup, the registration is going to fail with:
~~~
"ERROR: Validation failed: Ip does not match selected subnet".
~~~

So the user has to workaround it somehow:

a) Rename the NICs so the order changes.
b) Register without hostgroup, correct networking bits, assign hostgroup.
c) Use bootstrap.py instead of registration template. Bootstrap script has '--ip' option that allows to choose primary NIC.

Options a) and b) are a big hassle. I believe if it's achievable via bootstrap.py then it should also be possible via Global Registration Template.

QE Tracker for https://issues.redhat.com/browse/SAT-8413
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2055588