Reduce backend data leakage on frontend

[alexluckett]

Proposed change

Reduces some of the data sent to the frontend for security purposes.

At the same time I noticed that the file upload JS only worked if you had registered forms-engine-plugin with a prefix, so this PR includes a fix for that too.

Jira ticket:

Type of change

• Bug fix
• New feature
• Breaking change
• Misc. (documentation, build updates, etc)

Checklist

• You have executed this code locally and it performs as expected.
• You have added tests to verify your code works.
• You have added code comments and JSDoc, where appropriate.
• There is no commented-out code.
• You have added developer docs in README.md and docs/* (where appropriate, e.g. new features).
• The tests are passing (npm run test).
• The linting checks are passing (npm run lint).
• The code has been formatted (npm run format).

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[alexluckett]

Merging this so main is fixed, I have an alternative solution to follow I'll put as a draft PR