chore(api): add field to schema in provision script

[ragingsquirrel3]

API integration tests were failing. This was because they use codegen models from amplify_test package, where another field was added to the schema. The provisioned backend didn't have that field, so appsync was giving some errors when trying to include in a selection set (which the model helpers will do from codegen models). To fix it, you can just add that field to the backend. This PR adds in provision script so it will be fixed in any newly provisioned backend.

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[codecov-commenter]

Codecov Report

Merging #1909 (2c9cbfa) into main (a88616f) will increase coverage by 2.75%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1909      +/-   ##
==========================================
+ Coverage   45.13%   47.88%   +2.75%     
==========================================
  Files         369      373       +4     
  Lines       10012    10863     +851     
==========================================
+ Hits         4519     5202     +683     
- Misses       5493     5661     +168     

Flag	Coverage Δ
android-unit-tests	∅ <ø> (∅)
flutter-unit-tests	38.27% <ø> (ø)
ios-unit-tests	89.83% <ø> (-6.94%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
..._ios/example/ios/unit_tests/RestApiUnitTests.swift	85.16% <0.00%> (ø)
...plify_api_ios/example/ios/Runner/AppDelegate.swift	0.00% <0.00%> (ø)
...s/example/ios/unit_tests/GraphQLApiUnitTests.swift	89.50% <0.00%> (ø)
...xample/ios/unit_tests/FlutterURLSessionTests.swift	58.49% <0.00%> (ø)