Consolidate agreement opt-ins during account creation

[AllanOXDi]

Summary

This PR aims to consolidate the sign-up experience for users in Studio. Currently, a first-time user has to agree to two mandatory opt-ins at sign-up Terms of Service and privacy policy these processes are separated and require users to complete multiple steps to fully sign up. Consolidating these processes into a single, cohesive flow will make it as simple and straightforward as possible for users to opt-in or sign up in Studio.
closes #3834

Manual verification steps performed

1. Navigate to sign in page > create account

Screenshots (if applicable)

Before

After:

figma

https://www.figma.com/file/1tQQ0Sw1yDjzO66hyjLVPM?node-id=556:4666#323944643

Contributor's Checklist

PR process:

• If this is an important user-facing change, PR or related issue the CHANGELOG label been added to this PR. Note: items with this label will be added to the CHANGELOG at a later time
• If this includes an internal dependency change, a link to the diff is provided
• The docs label has been added if this introduces a change that needs to be updated in the user docs?
• If any Python requirements have changed, the updated requirements.txt files also included in this PR
• Opportunities for using Google Analytics here are noted
• Migrations are safe for a large db

Studio-specifc:

• All user-facing strings are translated properly
• The notranslate class been added to elements that shouldn't be translated by Google Chrome's automatic translation feature (e.g. icons, user-generated text)
• All UI components are LTR and RTL compliant
• Views are organized into pages, components, and layouts directories as described in the docs
• Users' storage used is recalculated properly on any changes to main tree files
• If there new ways this uses user data that needs to be factored into our Privacy Policy, it has been noted.

Testing:

• Code is clean and well-commented
• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Any new interactions have been added to the QA Sheet
• Critical and brittle code paths are covered by unit tests

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Reviewer's Checklist

This section is for reviewers to fill out.

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[bjester]

Please revert the contactMessage string back to its original form-- see my comment about the reasons why. Also, it appears some JS tests for account creation are failing, and they likely need updated to handle only one checkbox. You can run it with:

yarn run test-jest contentcuration/contentcuration/frontend/accounts/pages/__tests__/create.spec.js

[bjester]

Great work, Allan!