Workload Identity -> Identifier

[yaronf]

And in general consolidate the Workload Identity section with the architecture I-D, or possibly remove the section altogether.

[PieterKas]

Commenting as an identity enthusiast as opposed to WIMSE co-chair:

Section 3 should be renamed as Workload Identifier since the section is all about defining the workload identifier format. I found it useful to have the definition of the identifier format here, but agree that it should not be at odds with the architecture documents definition. @joe-venafi it may make sense to have only one definition - if it is in the architecture document, it would be sifficinet to reduce this section to simply reference the definition of a workload identifier in the architecture doc.