Add script to generate diffs between a cluster and the local branch

[Kidswiss]

Summary

make render-diff will run a script, that connects to the current cluster in KUBECONFIG and runs a diff against the current AppCat branch.

It leverages Crossplane's crank utility to render the result of a single function reconcile. It then uses dyff, a YAML and K8s aware diff tool, to actually show the diff itself.

Limitations: it can currently only generate a single reconcile run against the current state. If a function needs multiple reconciles to change the desired state, it won't show up in the diff.

Checklist

• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency
  as they show up in the changelog
• Update tests.
• Link this PR to related issues.