Fixes #19706 - don't treat DHCP leases as conflicts

fixes #17533 - provision dhcp for bond child macs

Fixes #12634 - New HW Model flag pxe_loader

Implementation of

https://github.com/theforeman/rfcs/blob/master/text/0001-PXE-Booting-UEFI.md

In short, new host/hostgroup flag PXE loader is added to specify TFTP
DHCP filename and Foreman now orchestrates all PXE-capable templates...

fixes #14638 - Refactor Subnet into STI to allow different subnet types

Fixes #13725 - DHCP MAC conflicts are reported

fixes #10020 - add next-server/filename attrs to provision NIC DHCP record

A host's DHCP record used to be constructed with PXE attributes in
Orchestration::DHCP, but moved to Nic::Managed during 43c4bd7. Nic::Managed
didn't add PXE attributes, so this commit adds these when provision? is set....

Fixes #8727 - DHCP validation does not fail on discovered leases

Refs #3809 - Enable cop StringConversionInInterpolation

Fixes #7971 - DHCP hostname commutative conflict fix

Refs #3809 - Use parentheses in method definitions