test (kubernetes-client-api) : Remove redundant methods and nested cl…

…asses in ConfigTest

- Remove `@Nested` class BuildConfigured as it doesn’t have any common setup, teardown blocks
- Remove these tests as they were already covered by ConfigSourcePrecedenceTest:
  - `testOverrideViaSystemProperties`
  - `testSystemPropertiesAndBuilderGetMorePrecedenceOverKubeconfig`
- Rename tests with legacy names starting with `testXXXX`
- Add `@DisplayName` annotation for tests wherever applicable
- Remove `assertConfig` method and inline assertions in tests wherever it’s getting used
- Remove abstract test class introduced in fabric8io#6157 `AutoConfiguredDisabledScenarios`, duplicate tests so that it’s more clear in case of failure

Signed-off-by: Rohan Kumar <[email protected]>