Fix Code Editor Not Clearing After Import Submission

[Marcus-Goectau]

🗣 Description

Looking at the code, it appears the intended behavior of the “import another module” button was to clear the form completely to prepare for an additional module import. However, the codeModel was not being properly reset, allowing for invalid JSON to be sent to the API on subsequent submissions. This has been fixed and a warning has been introduced next to the "import another module" button so it is clear that the code editor is reset after each submission.

💭 Motivation and context

bug/CSET-139

🧪 Testing

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.

✅ Pre-merge checklist

• Revert dependencies to default branches.
• Finalize version.

✅ Post-merge checklist

• Create a release.