Ads forwarded to the view collector should have optional projection
It should be possible to use a projection for updates forwarded to a VIEW_COLLECTOR. The use case for this is when the VIEW_COLLECTOR mechanism is use to build a collector tree, the baby collectors should be able to forward to the top collector only those attributes needed by the negotiator.
When preemption is disabled, the negotiator normally uses a projection expression for ads that it fetches, that same projection expression could be used for ads forwarded from the baby collector.
An new knob, COLLECTOR_FORWARD_PROJECTION will be added. It will have a no default value. it should be an expression evaluated in the context of the ad being forwarded. If an administrator wishes to minimize the amount of data forwarded to the top level collector, they can set this knob to
when NEGOTIATOR_CONSIDER_PREEMPTION is false. This set of attributes are those needed by the negotiator, and those needed by condor_status.
This looks good.