Honor artifact dir param

What does this MR do?

This fixes issue reported in gitlab-org/gitlab#351056, where value set in ANALYZER_ARTIFACT_DIR or --artifact-dir command line is ignore when specifying the output path. This also create artifact directory structure if not exists.

Limitation Only support relative path

What are the relevant issue numbers?

gitlab-org/gitlab#351056

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
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer