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. https://github.com/auth0/node-jsonwebtoken/issues/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

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 48.46%. Comparing base (ec9a2ba) to head (40b60a4). :warning: Report is 715 commits behind head on dev.

Additional details and impacted files

@@             Coverage Diff             @@
##              dev   #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     

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