Fix timeout

What does this MR do?

Fix DAST timeout when $DAST_TARGET_AVAILABILITY_TIMEOUT is used. The current version of dast uses a loop around curl, which can result in a longer timeout than $DAST_TARGET_AVAILABILITY_TIMEOUT (if the connection succeeds, but the server doesn't send any respond, curl will wait). This change ensures that the initial connection takes no longer than $DAST_TARGET_AVAILABILITY_TIMEOUT.

What are the relevant issue numbers?

N/A

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
  • [-] CI Templates (to be removed)
  • • ] Vendored CI Templates (also in CE)
  • [-] Ensure that all of the ENV vars supported are propagated to Docker containers upon docker run in job definitions
• Conforms to the code review guidelines
• [-] Conforms to the Go guidelines
• Security reports checked/validated by reviewer