Resolve "Use Helm 3 in review apps"

What does this MR do?

Updates CI to use Helm 3. Uses the Helm 3 base image from gitlab-org/gitlab-build-images!336 (merged).

Implementation plan: thread

Related issues

#2350 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened

Closes #2350 (closed)