chore: refactor controller_test

[pijusn-cast]

I wanted to refactor this test outside my primary task in order to isolate changes and avoid huge diffs. I want this test to:

• easily accept samples having the same kind but different GV (currently, we don't have such sample as we don't support them yet)
• support using unstructured.Unstructured runtime type (which is why data is compared using JSON helpers rather than plain bytes).

Also, note:

• To maintain consistency, updated other test cases to use the same pattern to compare the serialised JSONs.
• Added TypeMeta values everywhere to be more consistent as we start caring about these for some types.