API support for polling ingest status

[bnlawrence]

Use Case:

Cylc job running on remote system wishes to ingest data into the NLDS, and remove data on that system when NLDS has the data. That requires something like:

job - > nlds : load manifest
nlds -> job: job id
repeat:
   job -> nlds: is it loaded?
   until: ndls -> job: yes
job deletes local copy of data described by manifest

which requires client-side support, which may or may not be planned for.

[jackleland]

Unless I'm misunderstanding, this is already covered by a bash call to stat with the transaction_id flag set and some awk-ing of the output. i.e.
nlds stat -t d227910a-f735-4c5f-ae51-c419a5648d9a | grep job_state | awk '{ print $3 }'

or some equivalent python call to the clientlib.

We could make an explicit 'is it loaded?' API endpoint which returns a boolean for cleanliness?