chore: refactor crd validation tests to deduplicate boilerplate

[czeslavo]

What this PR does / why we need it:

Refactors the tests under test/crdsvalidation to deduplicate the boilerplate needed for every single CRD type. This pattern of testing proved to be flexible enough to run any scenario we wanted to check, therefore I think it's worth extracting this as a common suite type.

What has been done:

• the nested structure of tests was flattened as we no longer need isolation for the test case types named the same in every test package; now every CRD has its own single crdname_test.go file under tests/crdsvalidation
• a generic CRDValidationTestCase was extracted along with a grouping type CRDValidationTestCasesGroup
• all existing test cases were migrated to use the CRDValidationTestCasesGroup

What hasn't been done (aka excuses for the changes volume):

• no new tests were added
• no modifications to the existing test cases were done apart from:
  • renaming the <CRDName> field in the test case to TestObject
  • moving the <CRDName>Status contents from test cases that had it to the TestObject itself

Which issue this PR fixes
Enabler for #29.

[pmalek]

🏅

Just 1 nit about the shared client.