Use vue test utils for Kubernetes applications component tests

What does this MR do?

mountComponent has been deprecated, but the tests for the Kubernetes applications component still uses it. This MR changes it to use vue-test-utils' mount and shallowMount. Please note that the purpose of this MR is to switch from mountComponent to mount/shallowMount. It does not address, nor is it intended to address the robustness of the tests themselves.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability 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
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done