Convert milling GIF API endpoint into workflow instead

[tieneupin]

As part of ensuring the pipeline is modular, and to allow for the step to be rerun easily in the event of failure, the make_milling_gif API endpoint was converted into a workflow that is consumed from RabbitMQ and acked/nacked by the feedback_callback function in the backend server.

[codecov]

Codecov Report

❌ Patch coverage is 79.41176% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.10%. Comparing base (8f00dbf) to head (1261025).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #829   +/-   ##
=======================================
  Coverage   53.10%   53.10%           
=======================================
  Files          99      100    +1     
  Lines       10817    10837   +20     
  Branches     1432     1436    +4     
=======================================
+ Hits         5744     5755   +11     
- Misses       4769     4776    +7     
- Partials      304      306    +2     

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