Generate container analysis API

[JustinBeckwith]

I was looking at making sure we have LICENSE files everywhere, and noticed this repo exists: https://github.com/googleapis/google-cloud-php-container-analysis/

But ... there was nothing in it! We have that API generated for most other languages, so we should probably tick that box for PHP as well. I went ahead and archived the repo for now since it's empty (and has been around over a year), but feel free to bring it back to life when ready!