scheduler: tag executors with app id

[csegarragonz]

Thus far, we tagged executors with the (user, function) pair. This is needed in multi-threaded environments, where different threads must share the same executor. However, using only the (user, function) pair prevents the execution concurrent applications with the same pair.

Instead, the correct thing to do is to track applications using the (user, function) pair in conjunction with the application id.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.33%. Comparing base (ddba013) to head (c228c0f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #434   +/-   ##
=======================================
  Coverage   81.33%   81.33%           
=======================================
  Files         117      117           
  Lines        8233     8233           
=======================================
  Hits         6696     6696           
  Misses       1537     1537           

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