DAST excludes Browserker URLs that are out of scope

What does this MR do?

When Browserker spiders, it indexes all the links of the page, including those outside of the target website. This MR updates ZAP to only scan hosts that are included in DAST_BROWSERKER_ALLOWED_HOSTS.

What are the relevant issue numbers?

gitlab-org/security-products/analyzers/browserker#50

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