This big commit improves the jobs API in a way that now we can completely abstract away over a JobLog. In particular, here is the summary of what has been done:

• Our MonadJobStatus has a bigger API surface, to accommodate the fact we want our API to be potentially polymorphic over the JobEventType. Now in principle we could swap a JobLog for something different, change it once at the instance declaration and off we go;

• We now have a minimal, yet complete API to deal with tracking progress. In particular:

  -- | Start tracking a new 'JobEventType' with 'n' remaining steps.
  markStarted :: Int -> JobHandle m -> m ()

  -- | Mark 'n' steps of the job as succeeded, while simultaneously substracting this number
  -- from the remaining steps.
  markProgress :: Int -> JobHandle m -> m ()

  -- | Mark 'n' step of the job as failed, while simultaneously substracting this number
  -- from the remaining steps. Attach an optional error message to the failure.
  markFailure :: Int -> Maybe T.Text -> JobHandle m -> m ()

  -- | Finish tracking a job by marking all the remaining steps as succeeded.
  markComplete :: JobHandle m -> m ()

  -- | Finish tracking a job by marking all the remaining steps as failed. Attach an optional
  -- message to the failure.
  markFailed :: Maybe T.Text -> JobHandle m -> m ()

This allows for a clean tracking on progress, without all the visual cluttering. Practical example:

graphRecompute :: (FlowCmdM env err m, MonadJobStatus m)
               => UserId
               -> NodeId
               -> JobHandle m
               -> m ()
graphRecompute u n jobHandle = do
  markStarted 1 jobHandle
  _g <- recomputeGraph u n Spinglass BridgenessMethod_Basic Nothing Nothing NgramsTerms NgramsTerms False
  markComplete jobHandle

This MR could in principle be merged as-it-is, although there is a bit of repetition I had to introduce due to the runCmdGargDev which would be nice to eliminate, but that's not a blocker for getting this MR reviewed and merged.