Integration without *testing.T

**What would you like to be added**:
The ability to intigrate with kuttll without *testing.T.

**Why is this needed**:
Right now, to use a kuttll Harness the developer is required to have an instance of testing.T struct. In many cases, such instance isn't avaliable.
For example, tests writin using Ginkgo doesn't have such an object.

One possible solution is defining an interface instead of using the strcut directly - this will allow users to define their own implementation (https://onsi.github.io/ginkgo/#using-third-party-libraries).

I think this is a very cool project and would like to integrate it as a part of an existing e2e, but right now I would need to call a subprocess to use kuttl. I think that the dependency on *testing.T is a bit too specific

Start at the Kuttl Harness API and trace where *testing.T is required. Compare that integration point with Ginkgo's third-party library guidance, then define the smallest compatible way to use the Harness without *testing.T while preserving existing testing.T usage; done means an e2e test can integrate Kuttl from Ginkgo without a subprocess.

Written by the indexing model from the issue text.