Improve API response handling for token based upload

[Xpirix]

This will improve the API for uploading a new plugin version with a Token.
For API/Token Requests:

• Returns JSON responses instead of HTML
• Uses proper HTTP status codes:
  • 201 - Version created successfully
  • 200 - Version updated successfully
  • 400 - Validation errors or exceptions
  • 405 - Method not allowed (non-POST requests)

Response Structure for Success:

{
  "success": true,
  "message": "The Plugin Version has been successfully created.",
  "version": "1.0.0",
  "plugin_id": 123,
  "version_id": 456,
  "approved": true,
  "security_scan": {
    "status": "passed",
    "critical_count": 0,
    "warning_count": 2,
    "info_count": 5,
    "scan_url": "http://..."
  },
  "warnings": ["..."]
}

Response Structure for Errors:

{
  "success": false,
  "error": "Validation failed",
  "errors": {
    "field_name": ["error message"]
  }
}

Cc @3nids , Will this be handled automatically by the qgis-plugin-ci? I see that it uses response.raise_for_status() so any status codes other than 200-299 should raise an exception.

[3nids]

cool, thanks again!

[Guts]

Yipeee you're my heroe @Xpirix!