refactor(toolkit): move aws-auth and plugin to shared package

[mrgrain]

This intentionally only moves the source, and not the tests. Tests will be moved later to keep the diff size managable. Code is still tested as the tests are still running from aws-cdk package.

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.93%. Comparing base (586e1b3) to head (5bb9728).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #327      +/-   ##
==========================================
- Coverage   86.96%   86.93%   -0.04%     
==========================================
  Files         220      206      -14     
  Lines       35648    34059    -1589     
  Branches     4369     4188     -181     
==========================================
- Hits        31003    29609    -1394     
+ Misses       4545     4358     -187     
+ Partials      100       92       -8     

Flag	Coverage Δ
suite.unit	86.93% <100.00%> (-0.04%)	⬇️

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[mrgrain]

exempting from integ tests. most passed, only one failed likely due to config of the new atmosphere service. I'm taking the risk.