refactor(cli): make notices display autodect part of yargs

[mrgrain]

configuration.settings.get(['notices']) looks like it should have the correct value already and subsequently shouldDisplayNotices also implies this. But the previous code had the auto-detection logical after this and so the config could unexpectedly be undefined.

This PR fixes this by moving the auto-detection logic into yargs default parsing.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.25%. Comparing base (1d4fd87) to head (c9435c3).

Files with missing lines	Patch %	Lines
packages/aws-cdk/lib/cli/cli.ts	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #450      +/-   ##
==========================================
+ Coverage   79.18%   79.25%   +0.06%     
==========================================
  Files          54       54              
  Lines        6895     6897       +2     
  Branches      772      772              
==========================================
+ Hits         5460     5466       +6     
+ Misses       1417     1413       -4     
  Partials       18       18              

Flag	Coverage Δ
suite.unit	79.25% <77.77%> (+0.06%)	⬆️

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