Product Opener/Automatic deployment

Plan to make it possible to deploy any PR to a test instance of Product Opener using docker.

Commit to a PR >> GitHub Actions >> Tests >> Deploys using Docker to an outside service or to a test server we'd have to maintain. Example URL:

pr-2232.test.openfoodfacts.org

We'd need a mechanism to destroy the test instances, or possibly a mechanism to launch the custom generated Docker files.