Default /signup page to Create Account instead of Sign In to improve UX

[lfilip-ivaal]

🗣 Description

Update the Amplify Authentication component in AuthLoginCreate.tsx on /signup and /registration to default to the Sign Up tab.

💭 Motivation and context

This upgrade is to default the signup page to the signup section of the AWS Amplify Authentication Component. This creates an easier time for the User to signup without being confused by the sign-in section being presented when they would like to register. Fixes #2546

🧪 Testing

Ran regular tests and checks in Github actions.

✅ Pre-approval checklist

• [X] This PR has an informative and human-readable title.
• [x] Changes are limited to a single goal - eschew scope creep!
• [X] I have read the CONTRIBUTING document.
• [X] These code changes follow cisagov code standards.
• [X] All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• [X] Tests have been added and/or modified to cover the changes in this PR.
• [X] All new and existing tests pass.

✅ Pre-merge checklist

• [ ] Revert dependencies to default branches.
• [ ] Finalize version.

✅ Post-merge checklist

• [ ] Create a release.