Limit the number of URLs shown in an aggregated vulnerability

What does this MR do?

This MR limits the number of URLs listed in an aggregated vulnerability's details section to 50 by default. It also adds the environment variable DAST_AGGREGATED_VULNERABILITIES_REPORTING_LIMIT to allow the user to set that value manually if required. Setting DAST_AGGREGATED_VULNERABILITIES_REPORTING_LIMIT to 0 will remove the limit and allow all URLs to be listed.

What are the relevant issue numbers?

gitlab-org/gitlab#254043 (closed)

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