Make DAST updated and released on a weekly basis

What does this MR do?

Enables re-building major, latest tag and x-y-stable tags on scheduled pipelines in order to release DAST on a weekly basis (because zap2docker/weekly is updated on a weekly basis). For that, it:

• Adds a job to build major automatically for scheduled pipelines
• Adds a job to build the latest tag automatically for scheduled pipelines
• Makes all deploy jobs (tag latest and x-y-stable) run also on scheduled pipelines

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/11213

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