GitHub Action for publishing SIG meeting videos on YouTube

[alanwest]

Fixes #863

Here it is folks. I've been running this action from my own fork of the community repo for months now.

I've modified the tool to retrieve its configuration from a set of environment variables. The values of these variables need to be stored as secrets on the repo.

The OAuth credentials required for using the YouTube API is kinda a pain as they require a Google account and they expire periodically. There may be some options to get around this. At this point it probably just makes sense for me to meet with one of the maintainers to figure out the best way to proceed.

In the meantime, this tool is running happily on my fork every 6 hours.