Store responses from outbound push tasks in couch

[michaelkohn]

As a system admin, I want to see the API responses for an outbound push task in couch so I can monitor (and potentially action upon*) the results of certain tasks.

An example use case for this is pushing dataSets to DHIS2. Even when the transmission is successful, the response gives us useful information about things like how many values were overwritten, if values were ignored, etc...

Another use case for this might be creating person and patient records in OpenMRS, whereby the response to the API call will include (amongst other things) the OpenMRS ID of the created person or patient.

*When I say “action upon”, an example would be to store the returned OpenMRS Patient ID against the user in the CHT.

[SCdF]

Related to #6158 in terms of decisions around extending outbound push functionality