Bump helm and kubectl for Kubernetes integration

What does this MR do?

Bump the helm and kubectl used in our Kubernetes integration, used e.g. to install apps.

Note I have only bumped to the latest patch of the v1.11 series for kubectl as GKE clusters are still on 1.10/1.11

See https://github.com/helm/helm/releases/tag/v2.12.3 and https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG-1.11.md for changelogs

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/52791

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