feat: use sub:username identity claim by default when persisting behind a feature flag

[danielleadams]

Description of changes

This pull requests does the following:

• persists "sub::username" format on Mutation requests
• adds a feature flag that is default for existing apps to use "username"
• adds a warning for current owner based auth on compile either explicitly use "username" if they want to keep using it

Description of how you validated changes

• yarn test
• e2e tests in a later PR
• manual testing matrix

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies

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

[akshbhu]

Some minor comments but overall LGTM

[akshbhu]

we can remove this

[danielleadams]

It was reordered, not added, so I'll leave it and we can remove non words in another PR.

[marcvberg]

Looks like some snapshots need to be updated, otherwise seems good

[codecov-commenter]

Codecov Report

Merging #10196 (47bbb83) into master (846048c) will increase coverage by 0.18%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master   #10196      +/-   ##
==========================================
+ Coverage   54.25%   54.43%   +0.18%     
==========================================
  Files         849      854       +5     
  Lines       46939    47026      +87     
  Branches    10004    10027      +23     
==========================================
+ Hits        25467    25599     +132     
+ Misses      19456    19413      -43     
+ Partials     2016     2014       -2     

Impacted Files	Coverage Δ
...mation/service-walkthroughs/appSync-walkthrough.ts	15.30% <0.00%> (ø)
...r-utils/awscloudformation/utils/layerCloudState.ts	15.49% <0.00%> (-0.23%)	⬇️
...amplify-category-geo/src/service-utils/mapUtils.ts	57.69% <ø> (ø)
...amplify-cli-core/src/feature-flags/featureFlags.ts	80.85% <ø> (ø)
.../extensions/amplify-helpers/update-amplify-meta.ts	14.01% <0.00%> (ø)
...auth-transformer/src/__tests__/acm-test-library.ts	100.00% <ø> (ø)
...-auth-transformer/src/resolvers/mutation.create.ts	95.45% <ø> (+6.81%)	⬆️
...-auth-transformer/src/resolvers/mutation.update.ts	95.65% <ø> (+6.52%)	⬆️
...y-graphql-auth-transformer/src/resolvers/search.ts	68.31% <ø> (ø)
...ql-auth-transformer/src/resolvers/subscriptions.ts	100.00% <ø> (+4.16%)	⬆️
... and 58 more

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[danielleadams]

@marcvberg this has been rebased

[marcvberg]

LGTM

[danielleadams]

When #10222 is merged, these tests will pass (they are due to mismatched snapshots)