Suppress uninteresting parts of long object diffs

[porridge]

What happened:

Assert on something like a Deployment, for example:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: central
status:
  availableReplicas: 1

and the deployment's spec is non-trivial, you get this massive literally a few hundred lines long diff which mostly consists of metadata.managedFields (see #370) and contents of spec which is mostly irrelevant with the above assertion. This verbosity makes it somewhat hard to navigate the kuttl output, especially if you assert against several such deployments in single step.

What you expected to happen:

The pretty-diff output should omit long unnecessary fields.

How to reproduce it (as minimally and precisely as possible):

See the test case in the PR which is coming up soon.