feature: add tests

[reginapizza]

Is your feature request related to a problem? Please describe.
There is currently no unit tests or e2e tests, it would be great to add some so that we can run it as part of a CI.

Describe the solution you'd like
Add test suite to the must-gather component. At minimum it should check that the script runs (and writes to error file for cases when it shouldn't run, such as when cluster isn't an openshift cluster and/or when kubectl or oc aren't installed) and writes output information to files.

Corresponds to GITOPS-2579