feat: ETLng task manager

[godexsoft]

Implementation of a task manager for ETL ng.
There are a couple TODOs left that require some changes in AsyncFramework to implement properly - I'd like to leave it for a separate PR and then fix those TODOs in a later stage of ETL ng implementation.

[codecov]

Codecov Report

Attention: Patch coverage is 84.52381% with 13 lines in your changes missing coverage. Please review.

Project coverage is 71.70%. Comparing base (3e200d8) to head (eebaf47).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/etlng/impl/TaskManager.cpp	78.84%	4 Missing and 7 partials ⚠️
src/util/StrandedPriorityQueue.hpp	90.47%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1843      +/-   ##
===========================================
+ Coverage    71.62%   71.70%   +0.08%     
===========================================
  Files          330      333       +3     
  Lines        13413    13488      +75     
  Branches      6826     6861      +35     
===========================================
+ Hits          9607     9672      +65     
  Misses        1921     1921              
- Partials      1885     1895      +10     

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[cindyyan317]

LGTM