Error when user is not licensed for DAST

What does this MR do?

When a user attempts to use DAST but is unlicensed, the console shows the error message.

Error: Your GitLab project is not licensed for DAST.

Since this change adds only a thin layer of security and can be easily overridden, DAST will continue to function if GITLAB_FEATURES is not set. This allows developers to continue working on DAST without disruption and tests to function as expected.

What are the relevant issue numbers?

This MR relates to #290958

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Job definition example
  • Vendored CI Templates (also in CE)
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer