[FEATURE] Add a Message/Job Status summary endpoint

[imyousuf]

Is your feature request related to a problem? Please describe.
There is no way to understand the status of messages and jobs by channel; so it difficult to say what is the current status summary.

Describe the solution you'd like
We want an endpoint that would summarize by channel number of messages dispatched vs non-dispatched and then by consumers jobs queued, inflight, delivered and dead.

Describe alternatives you've considered
Currently the alternate is to run query in the DB with group by

Additional context

[imran2140]

We can add a stats endpoint for consumers (/channel/<channelId>/consumer/<consumerId>/stats) that expose job related metrics for a consumer. The initial implementation can add job count by status, which would be useful for monitoring number / ratio of dead jobs. The endpoint should require date filter parameters to avoid doing aggregation on all time jobs.

Parameter	Type
createdSince	required, iso date time (inclusive)
createdUntil	optional, iso date time, default to current datetime (inclusive)

Output

{
    "JobStatus": {
        "<Status>": "<Count (int)>"
    }
}

[imyousuf]

Since we implemented pruning, I am not sure if date filtering makes sense. Since only messages/jobs that will remain in DB would be dead messages; so they should be reenqued and processed manually in any case. So leaving out date based filtering capability in first iteration.