fix(amplify-graphiql-explorer): amplify mock with Cognito User Pool

[aoi]

Description of changes

This bug is caused by jsonwebtoken's verify method.
The issue is here. auth0/node-jsonwebtoken#863
There is no choice but to use an alternative library.

I've replaced jsonwebtoken to jsrsasign.
I chose jsrsasign for the following reasons:

1. jsrsasign is featured on jwt.io which is a trustworthy website. https://jwt.io/libraries?language=JavaScript
2. Since jose requested async/await, jsrsasign is less affected by the fix. There is not much difference in functionality.

Issue #, if available

aws-amplify/amplify-category-api#1646 12905

Description of how you validated changes

I've confirmed amplify mock with Cognito User Pool works.
The GraphiQL page is shown propery. The queries work.

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
• Pull request labels are added

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

[codecov-commenter]

Codecov Report

Merging #12906 (ab4acb7) into dev (ec9a2ba) will increase coverage by 48.46%.
The diff coverage is 58.63%.

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@@             Coverage Diff             @@
##              dev   aws-amplify/amplify-cli#12906       +/-   ##
===========================================
+ Coverage    0.00%   48.46%   +48.46%     
===========================================
  Files        1296      837      -459     
  Lines      149743    38041   -111702     
  Branches     1296     7747     +6451     
===========================================
+ Hits            0    18436    +18436     
+ Misses     148447    18017   -130430     
- Partials     1296     1588      +292     

Impacted Files	Coverage Δ
...y-category-function/src/commands/function/build.ts	0.00% <0.00%> (ø)
...ify-category-function/src/events/prePushHandler.ts	33.33% <0.00%> (+33.33%)	⬆️
...ider-utils/awscloudformation/utils/layerHelpers.ts	21.80% <0.00%> (+21.80%)	⬆️
...er-utils/awscloudformation/utils/storeResources.ts	30.38% <ø> (+30.38%)	⬆️
...ib/S3AndCloudFront/helpers/configure-CloudFront.js	87.06% <ø> (+87.06%)	⬆️
...lify-category-hosting/lib/S3AndCloudFront/index.js	89.65% <ø> (+89.65%)	⬆️
...ifications/src/commands/notifications/configure.ts	0.00% <0.00%> (ø)
...e/src/amplify-node-pkg-detector/lock-file-types.ts	100.00% <ø> (+100.00%)	⬆️
.../src/amplify-node-pkg-detector/yarn-lock-parser.ts	100.00% <ø> (+100.00%)	⬆️
packages/amplify-cli-core/src/constants.ts	100.00% <ø> (+100.00%)	⬆️
... and 47 more

... and 1249 files with indirect coverage changes

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