add .github/workflows/cifuzz.yml

[DavidKorczynski]

Add CIFuzz workflow action to have fuzzers build and run on each PR.

This is a service offered by OSS-Fuzz where ipfs/go-datastore already runs (https://github.com/google/oss-fuzz/tree/master/projects/ipfs). CIFuzz can help detect regressions and catch fuzzing build issues early, and has a variety of features (see the URL above). In the current PR the fuzzers gets build on a pull request and will run for 300 seconds.

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[aschmahmann]

@ipfs/ipdx should this be here, or in Unified CI (https://github.com/protocol/.github)?

[galargh]

If it's a completely new workflow, I'd go with trying it out on a repo first and then proposing it for Unified CI.