Submit vulnerability form

What does this MR do and why?

This commit is part of a commit series which introduces a form to manually create a vulnerability. It adds the submit vulnerability button and handles the form submission.

Screenshots or screen recordings

Submitting a vulnerability

Form validation

Please note: The name input is also outlined with a red border. This gif is from a previous version.

How to set up and validate locally

1. Navigate to /-/security/vulnerabilities/new through the URL (should be a project scope)
2. Submit the form

In case it's successful, it should redirect to the newly created manual vulnerability. In case it's failed, it should display an alert.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #301003 (closed)