[#64583056] LoadBalancerService generator

This is cherry-picked and rebased from a separate branch, where the generator has been tested against a live VSE -- so is essentially complete.

I've added tests for the Pool and VirtualServer defaults, to ensure that the 'minimal config' path does not cause NilClass exceptions or similar. It serves to document the minimal configuration, but in truth may not actually load correctly into a live VSE -- it should be refined, but is a valid starting point.