Scale workers

[ahopkins]

This PR adds the ability to scale from the inspector or the multiplexer.

Resolves #2616

[codecov]

Codecov Report

Base: 88.574% // Head: 88.614% // Increases project coverage by +0.040% 🎉

Coverage data is based on head (b8e4a7e) compared to base (13e9ab7).
Patch coverage: 95.312% of modified lines in pull request are covered.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2617       +/-   ##
=============================================
+ Coverage   88.574%   88.614%   +0.040%     
=============================================
  Files           81        81               
  Lines         6634      6684       +50     
  Branches      1130      1142       +12     
=============================================
+ Hits          5876      5923       +47     
- Misses         522       524        +2     
- Partials       236       237        +1     

Impacted Files	Coverage Δ
sanic/worker/manager.py	92.810% <94.000%> (-0.110%)	⬇️
sanic/worker/inspector.py	98.924% <100.000%> (+0.074%)	⬆️
sanic/worker/multiplexer.py	100.000% <100.000%> (ø)
sanic/worker/process.py	88.888% <100.000%> (+0.124%)	⬆️

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