Draft: Use same user as baseimage

Related Issue(s)

• gitlab-org/gitlab#288010 (closed) (see for more details)

What does this MR do?

• switches zap user over to browserker

Why

• when i mount the volume it chowns /zap/work to browserker:staff (1000:50) which results in /zap/wrk not being writable for the zap user.

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