COST-1165: Add Priority worker/queue.

[myersCody]

How to Test

Testing Sources Delete

1. Bring up the koku server with:

docker-compose -f testing/compose_files/docker-compose-multiworker.yml up

2. Using the sources api, add a source. (If you need help with this step feel free to reach out)
3. Using the sources api, delete a source and watch the priority-worker logs. Example:

priority_worker    | [2021-03-18 18:08:40,743] INFO 5ce0e4d2-7ccc-4bfc-a412-f3674730ecab Deleting Provider 7b848818-e4c8-43d4-944f-56ae3b50c4d9 for Source ID: 2
priority_worker    | [2021-03-18 18:08:40,743: INFO/ForkPoolWorker-1] Deleting Provider 7b848818-e4c8-43d4-944f-56ae3b50c4d9 for Source ID: 2

Testing Cost Model Updates

1. Bring up the koku server with:

docker-compose -f testing/compose_files/docker-compose-multiworker.yml up

2. Add a source
   Note: This one does not have to be through the sources api, it can be any source.
3. After the source is added, add a cost model by posting the json to the cost model endpoint.
   Then check the logs to make sure the priority-worker picked up the cost-model update:

priority-worker    | [2021-03-22 15:54:27,257: INFO/ForkPoolWorker-1] [masu.processor.tasks.update_cost_model_costs(c16201d0-0a2a-4c3a-9667-c92a1c38a38f via c16201d0-0a2a-4c3a-9667-c92a1c38a38f)] update_cost_model_costs called with args:
priority-worker    |  schema_name: acct10001,
priority-worker    |  provider_uuid: 595e8cde-0dfe-4083-83fa-0bd30de28867

e2e changes: https://github.com/RedHatInsights/e2e-deploy/pull/2896

[codecov]

Codecov Report

Merging #2741 (5abbeed) into master (7246f95) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff           @@
##           master   #2741   +/-   ##
======================================
  Coverage    94.7%   94.7%           
======================================
  Files         289     289           
  Lines       22364   22365    +1     
  Branches     2550    2550           
======================================
+ Hits        21178   21179    +1     
- Misses        714     716    +2     
+ Partials      472     470    -2     

[maskarb]

lgtm!