Fuzzing: Initial commit

[AdamKorcz]

Adds the initial setup for fuzzing for the kustomize-controller.

It is currently WIP, but sharing in case anyone wants to test it or have comments.

To run the fuzzer in this PR:

git clone --branch fuzz1 https://github.com/AdamKorcz/kustomize-controller
cd kustomize-controller/fuzz
sudo docker build . --tag flux-fuzzing-image

The fuzzer will now run.

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Other fuzzing PRs in the Flux ecosystem:

• Fuzzing: Initial set up source-controller#443
• Fuzzing: Initial commit pkg#150
• Fuzzing: Initial commit notification-controller#250

[stefanprodan]

Superseded by #536