Add a new 'workload name' label override (#3374)

* Add a new 'workload name' label override

Today, we have a "workload name" concept that ends up in metrics.
This is defaulted to deriving from deployment metadata (Deployment name,
etc).

This approach is not perfect. We cannot always derive an appropriate
name (for instance, a Pod can be created directly!). WorkloadEntry,
which often is equvilent to Pod, is also using the WE name -- generally
we would want a higher order name there.

To fix this, I propose we add a label to explicitly specify the workload
name. This format mirrors the existing canonical-{service,revision}
label.

* regen

Author: howardjohn