Resolve "Follow-up from !30458: create `kubectl_delete(args)`"

What does this MR do?

Follow-up: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30458#note_197694045

An idea for ~"technical debt" issue: create kubectl_apply(args) and kubectl_delete(args) methods to avoid possible typos and repeating kubectl apply -f string in the code.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Related to #65343 (closed)