Allow extra args for helm in Auto-DevOps

What does this MR do?

Allows specifying custom helm arguments for the deploy job in Auto-DevOps.

This MR is based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26171 and adds the required changelog/additions so we can get it merged. Credit goes to @tortuetorche for originally submitting this 👍

What are the relevant issue numbers?

• https://gitlab.com/gitlab-org/gitlab-ce/issues/56961
• Closes https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26171

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer