test: add gen2 e2e tests

[AaronZyLee]

Description of changes

Added Gen2 e2e tests for graphql-generator related command

• npx ampx generate outputs
• npx ampx generate forms
• npx ampx generate graphql-client-code

Codegen Paramaters Changed or Added

Issue #, if available

Description of how you validated changes

Unit and E2E tests passed. Link to E2E

Checklist

• [ ] PR description included
• [ ] yarn test passes
• [ ] Tests are changed or added
• [ ] Relevant documentation is changed or added (and PR referenced)
• [ ] Breaking changes to existing customers are released behind a feature flag or major version update
• [ ] Changes are tested using sample applications for all relevant platforms (iOS/android/flutter/Javascript) that use the feature added/modified
• [ ] Changes are tested on windows. Some Node functions (such as path) behave differently on windows.

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