chore: upgrade aws-amplify from v4 to v6

[0618]

Description of changes

When working on https://github.com/aws-amplify/amplify-cli/security/dependabot/201, I noticed that it's caused by the out-dated aws-amplify, so migrate it to v6.

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
• [ ] 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.