chore(ci): replace npm-cli-adduser with native npm config

[ashwinkumar6]

Description of changes

Context

On May 29, 2024 our e2e tests began failing due to a minor version upgrade of Node (18.20.3) breaking npm-cli-adduser. In order to unblock our pipeline we pinned the Node version to 18.20.2 (#13450).

Changes on this PR

• Remove pinned node version on ci, pick latest node 18 version
• Upgrade to verdaccio v6, v5 is deprecated
• Remove npm-cli-adduser and replace with native npm commands/config

Description of how you validated changes

• CI run: print node_modules/aws-amplify/package.json in TestApp to ensure packages from verdaccio are being pulled in
• CI full run

Alternative Implementation

Instead of using verdaccio in auth mode we can update the verdaccio config to be unauth to allow anyone to push and pull packages to it on ci. Implementation Reference

Checklist

• PR description included
• yarn test passes
• Unit Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

Checklist for repo maintainers

• Verify E2E tests for existing workflows are working as expected or add E2E tests for newly added workflows
• New source file paths included in this PR have been added to CODEOWNERS, if appropriate

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