fix: pass appsync specific directives to model gen

[yuth]

AppSync service has some custom directives defined in the service. These directives are defiend in
transformer, so the documents that have them pass graphql validation. Passing them to model gen
plugin from transformer to keep these directives in sync

Issue #, if available:

Description of changes:

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[codecov-io]

Codecov Report

Merging #3211 into master will increase coverage by <.01%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #3211      +/-   ##
==========================================
+ Coverage   59.41%   59.41%   +<.01%     
==========================================
  Files         254      254              
  Lines       12583    12587       +4     
  Branches     2465     2465              
==========================================
+ Hits         7476     7479       +3     
- Misses       4794     4795       +1     
  Partials      313      313

Impacted Files	Coverage Δ
...c-model-plugin/src/scalars/supported-directives.ts	100% <ø> (ø)	⬆️
...ackages/graphql-transformer-core/src/validation.ts	100% <100%> (ø)	⬆️
packages/graphql-transformer-core/src/index.ts	96.77% <75%> (-3.23%)	⬇️

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[github-actions]

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