Add fuzzing by way of ClusterFuzzLite

[DavidKorczynski]

This adds fuzzing by way of ClusterFuzzLite, which is a GitHub action that will perform a short amount of fuzzing for new PRs. The goal is to use fuzzing to catch bugs that may be introduced by new PRs.

I added a fuzzer that targets jsonsl_feed, and currently set the timeout of CFLite to 100 seconds. CFLite will flag if the fuzzer finds any issues in the code introduced by a PR.

I added instructions in the README.md on how to run the fuzzer locally (notice you'd have to adjust the repos until this PR is merged).