Allow user-supplied Server label mapping

[Ulexus]

In a follow-up to the #282 feature of standard Label Selectors, we should add the ability for users to specify custom labels which should be automatically applied to Servers which match certain other labels.

The idea is: apply new label X if a Server matches a given spec value.

For instance:

• if Server has field spec.cpu.version containing the string E-2124G, add label custom-cpu-class = small
• if Server has field spec.system.productName matching exactly SYS-5039MC-H12TRF, add label chassis = blade

We should probably scope the available match fields to only a specific set (spec.cpu, spec.system, etc) rather than make all of spec matchable.

This could be made into an optional ConfigMap or CRD, as appropriate, but it should not be a required item.