Replace links and references to Template Studio with Template Playground

[anablaz]

Closes #421

Changes

• Links and references to Template Studio have been replaced with Template Playground

Related Issues

• Issue #421

Author Checklist

• [X] Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• [ ] Vital features and changes captured in unit and/or integration tests
• [ ] Commits messages follow AP format
• [ ] Extend the documentation, if necessary
• [X] Merging to master from fork:branchname
• [ ] Manual accessibility test performed
  • [ ] Keyboard-only access, including forms
  • [ ] Contrast at least WCAG Level A
  • [ ] Appropriate labels, alt text, and instructions

[mttrbrts]

Added a few comments. I also don't think we need to update the older versions of the docs, right @mttrbrts / @dselman ?

Yes, that's right, we should only update the latest version. We can cut a new version of the docs once this is merged.

[anablaz]

Hi @DianaLease, would it be possible to get a re-review, please?