fix: update auth vnext validation to use private for oidc

[SwaySway]

Description of changes

• update validation to allow private to work for oidc
• updated unit test to verify

Issue #, if available

Description of how you validated changes

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.

[lazpavel]

LGTM

[codecov-commenter]

Codecov Report

Merging #8606 (9715ac9) into master (bd435e2) will increase coverage by 1.21%.
The diff coverage is 56.19%.

@@            Coverage Diff             @@
##           master    #8606      +/-   ##
==========================================
+ Coverage   55.92%   57.13%   +1.21%     
==========================================
  Files         695      728      +33     
  Lines       38881    41174    +2293     
  Branches     7871     8441     +570     
==========================================
+ Hits        21743    23524    +1781     
- Misses      16343    16838     +495     
- Partials      795      812      +17     

Impacted Files	Coverage Δ
...fy-appsync-simulator/src/schema/directives/auth.ts	18.42% <ø> (ø)
...ppsync-simulator/src/utils/auth-helpers/helpers.ts	80.95% <ø> (ø)
...egory-api/src/provider-utils/supported-services.ts	100.00% <ø> (ø)
packages/amplify-category-auth/src/index.js	15.74% <0.00%> (ø)
...ider-utils/awscloudformation/assets/string-maps.js	86.20% <ø> (ø)
...auth/src/provider-utils/awscloudformation/index.js	3.90% <0.00%> (ø)
...ils/awscloudformation/service-walkthrough-types.ts	100.00% <ø> (ø)
...udformation/service-walkthroughs/auth-questions.js	3.33% <0.00%> (ø)
...s/amplify-category-geo/src/commands/geo/console.ts	53.84% <0.00%> (+3.84%)	⬆️
...amplify-cli-core/src/feature-flags/featureFlags.ts	83.62% <ø> (ø)
... and 110 more

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