Finer grained status information

[m-mohr]

For large processes, the lack of information regarding the actual state of the process was criticized. A finer grained status information (e.g. percentage completed) was suggested but also seen as being difficult to realize for complex process chains. (Part of EODC Forum take-aways.)

Could be implemented as an additional optional field in the job information, e.g. completed: 75 for 75% complete.
It may only be added as status that is sent as a execution update in the context of the /jobs/{job_id}/subscription endpoint.

[m-mohr]

Implemented for both subscriptions (already available in v0.3) and job information.