Enable job merging

[jsvennevid]

Jobs that are submitted with a shared tag should be merged as part of the job consume process. This will allow many producers to schedule jobs and have a single consumer process them.

Use case:

• User input from web frontend (1-n instances) triggers job
• Job is scheduled and remains in queue for a little while before being claimed
  • While job is in queue, another job with the same tag is scheduled
  • Jobs pulled by the consumer are merged
• Response is posted to all producers from single job completion

[jsvennevid]

Suggested process:

• Claim lock for tag
  • If lock is available, create entry in hash table (containing producer queue) and schedule job
  • If lock is taken, grab job id from hash table, add producer to queue and listen for response
• When consumer claims job, unlock and collect producers from queue
  • When job completes, send response to all producers