[PTRun][Docs] Update new plugin checklist

[hlaueriksson]

Summary of the Pull Request

• Change target framework
• Remove x64
• Cleanup markdown

PR Checklist

• [x] Closes: #30879
• [x] Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• [ ] Tests: Added/updated and all pass
• [ ] Localization: All end user facing strings can be localized
• [x] Dev docs: Added/updated
• [ ] New binaries: Added on the required places
  • [ ] JSON for signing for new binaries
  • [ ] WXS for installer for new binaries and localization folder
  • [ ] YML for CI pipeline for new test projects
  • [ ] YML for signed pipeline
• [ ] Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

• The target framework for plugins should be net8.0-windows.
• The x64 platform target requirement is no longer correct.
• My markdown linter compained, so I did some cleanup

Validation Steps Performed

[Jay-o-Way]

Coincidentally, there's also pr #30920. Please choose or merge :)