Fuzzing: Initial commit

[AdamKorcz]

Adding a fuzzer and related Dockerfile.
It is currently WIP, but I am sharing here to keep the process open in case anyone wants to check it out.

To run the fuzzer:

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

[stefanprodan]

Superseded by #306