Merge consumer functional tests

[tomaszmichalak]

Is your feature request related to a problem? Please describe. We should use a single scenario for all tests. Then we can simply modify the behaviour with overloading mechanism (from knotx-junit5). With that approach we would not repeat the same configs in all files.

Tests to merge:

• KnotxConsumersIntegrationTest
• KnotxFragmentsDebugDataWithHandlebarsTest

Additional context

• https://github.com/Knotx/knotx-fragments/tree/master/handler/consumer