Fixes #31370 - multi-host stub template snapshots (#8149)

Our snapshot template render test and generator only supports one host stub (ipv4 single NIC redhat OS). In order to test more ERB codepaths, we need a way to create snapshots against multiple host stubs (e.g. IPv6, dualstack, static IPv4 or IPv6, debian family). In order to do that, template metadata can be extended to define list of host stubs to create and test snapshots against.

Snapshot files are now named ProvisioningTemplate/PXEGrub/Kickstart_default_PXEGrub.host4and6.snap.txt where host4and6 is the stub name, this implements the following for starters:

• host - the original simple host
• host6 - IPv6 provisioning NIC
• host4and6 - dualstack provisioning NIC
• host4static - single stack IPv4 with static network credentials
• host6static - single stack IPv4 with static network credentials

Refs #31370 - simplify factory traits

In 641c3f4a9b we've introduced a factory trait for smart_proxy factory,
but instead of adding it to parent factory we added to all its children.

This is fixing that and simplifying the factories.