Enhance Gatling plugin security and UI

[vedanthvdev]

• Add Spotless (v2.44.5) for code formatting and import management

  • Configure Google Java Format (v1.15.0)
  • Enable automatic removal of unused imports
  • Set import order: java, javax, org, com

• Improve report viewer security

  • Re-enable content filtering for XSS protection
  • Filter script tags, event handlers, and javascript URLs
  • Maintain security headers for additional protection

• Enhance report download UI

  • Add dedicated download section with clear heading
  • Improve link styling and layout
  • Add bullet points for better readability
  • Use consistent font sizes and weights

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed