Example estimation and progress for job completion

[binkley]

AS A caller of long-running REST jobs
I WANT an estimation of completion when available
SO THAT I can let the user know

AS A caller of long-running REST jobs
I WANT completion progress when available
SO THAT I can let the user know

Context

See http://farazdagi.com/blog/2014/rest-long-running-jobs/

Acceptance criteria

GIVEN a REST service for long-running jobs
WHEN I submit a new job
THEN the response should include an estimation of completion if an estimation is available

GIVEN a REST service for long-running jobs
WHEN I submit a new job
THEN the response should indicate unknown when an estimation is not available

GIVEN a long-running REST job
WHEN I poll for progress
THEN the response should indicate progress when progress is available

GIVEN a long-running REST job
WHEN I poll for progress
THEN the response should indicate unknown when progress is not available

[binkley]

Consider applying https://blog.acolyer.org/2017/01/13/incremental-consistency-guarantees-for-replicated-objects/.

The idea is an initial request for /queue/Brian or /greetings/Brian return placeholders awaiting completion, which then return the final response.