Publish helper.py to PyPI

It would be helpful to publish the [helper.py script](https://github.com/google/oss-fuzz/tree/master/infra#helperpy) to PyPI https://pypi.org/ to make it easier to install and run without having to clone the oss-fuzz repo.

In particular, setting up [ClusterFuzzLite](https://google.github.io/clusterfuzzlite/build-integration/#generating-an-empty-build-integration) is particularly awkward because you keep having to change working directory to run oss-fuzz/infra/helper.py.

https://setuptools.pypa.io/en/latest/userguide/quickstart.html#entry-points-and-automatic-script-creation

Review infra/helper.py and the linked setuptools guide on entry points and automatic script creation. The work is done when helper.py can be installed from PyPI and run without cloning oss-fuzz or changing into its directory, including for the ClusterFuzzLite setup described in the issue.

Written by the indexing model from the issue text.