Pass new fuzz targets to docker containers at runtime

[oliverchang]

Rather than requiring us to patch Dockerfiles with an ADD instruction to add the fuzz target to the filesystem. This is rather hacky and has a lot of gotchas (see e.g. #699)

This would be a lot cleaner and simplify a lot of our current infrastructure.

[oliverchang]

@DavidKorczynski @DonggeLiu