Add new DW directive for enabling nnf-dm

[bdevcich]

Users need a way to specify that they want to do data movement while their application is running with the Copy Offload API and nnf-dm.

The directive breakdown can then be used to communicate back to flux that the nnf-dm needs to be started.

[matthew-richerson]

As a reminder, the DirectiveBreakdown resource is part of DWS (not Rabbit SW), so the new field shouldn't be Rabbit specific. Something like "RequiredDaemons=[nnf-dm]" rather than "NeedsNnfDM=true".

[roehrich-hpe]

Closed with #177