feat: new package: @aws-cdk/cloud-assembly-api

[rix0rrr]

This package is going to contain the parts of cx-api that pertain to the CLI and the processing of Cloud Assemblies. First I've made copies of all parts of cx-api that actually are owned by the CLI instead of the library (that is: everything except feature flags and the environment variables that the Cloud Executable expects).

After the first release of this package, we're going to remove everything that's been copied from the cx-api package from there, so that this becomes the only source of it.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[github-actions]

Total lines changed 4240 is greater than 1000. Please consider breaking this PR down.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.71%. Comparing base (696dada) to head (799860d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1033   +/-   ##
=======================================
  Coverage   87.71%   87.71%           
=======================================
  Files          72       72           
  Lines       10087    10088    +1     
  Branches     1330     1330           
=======================================
+ Hits         8848     8849    +1     
  Misses       1214     1214           
  Partials       25       25           

Flag	Coverage Δ
suite.unit	87.71% <100.00%> (+<0.01%)	⬆️

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