[tools/shoestring]: add support for advanced customization of rest.json

[Jaguar0625]

 problem: shoestring only allows user to specify nodeMetadata property of rest.config
solution: allow user to provide differential config file that overrides defaults (similar to REST native support)

   issue: #1090

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.24%. Comparing base (c8d3ad8) to head (cc6270b).
Report is 2 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1091   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files         162      162           
  Lines        6618     6623    +5     
  Branches      143      143           
=======================================
+ Hits         6502     6507    +5     
  Misses        116      116           

Flag	Coverage Δ
explorer-nodewatch	98.40% <ø> (ø)
explorer-rest	99.25% <ø> (ø)
faucet-authenticator	100.00% <ø> (ø)
faucet-backend	98.91% <ø> (ø)
faucet-frontend	100.00% <ø> (ø)
lightapi-python	98.35% <ø> (ø)
tools-shoestring	96.86% <100.00%> (+<0.01%)	⬆️
tools-vanity	99.25% <ø> (ø)

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Files with missing lines	Coverage Δ
tools/shoestring/shoestring/commands/setup.py	100.00% <100.00%> (ø)
...string/shoestring/internal/ConfigurationManager.py	100.00% <100.00%> (ø)
tools/shoestring/shoestring/internal/Preparer.py	100.00% <100.00%> (ø)
...hoestring/shoestring/wizard/ShoestringOperation.py	100.00% <100.00%> (ø)
...oestring/shoestring/wizard/setup_file_generator.py	100.00% <100.00%> (ø)
...estring/shoestring/wizard/shoestring_dispatcher.py	100.00% <100.00%> (ø)

[Wayonb]

👍🏾