Add memory usage to metrics reports

What does this MR do?

this merge request pulls out some memory usage stats and puts them into the metrics report in order to track them over time.

Example Pipeline

https://gitlab.com/gitlab-org/security-products/dast/-/jobs/643350340

What are the relevant issue numbers?

gitlab-org/gitlab#227729 (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