Add CIFuzz integration

[DavidKorczynski]

Add CIFuzz workflow action to have fuzzers build and run on each PR. This is a service offered by OSS-Fuzz, on which Openssh already runs (https://github.com/google/oss-fuzz/tree/master/projects/openssh)

[daztucker]

I don't think this will work since we currently don't allow any third party workflows on the OpenSSH project.

[DavidKorczynski]

Okay - I am happy to leave this open in case your policy changes and feel free to close the issue if you prefer

[daztucker]

We now allowlist a Cygwin workflow for testing purposes, we could probably extend the allowlist and enable this now.

[daztucker]

Applied, thanks. I'm still fiddling with the allowlist settings.