Update source of poetry installation script

[sondrelg]

As of the latest poetry release (1.1.7) get-poetry is no longer the recommended installation script, and in the next minor release it will be fully replaced by install-poetry 🙂

[sondrelg]

Looks like https://github.com/tiangolo/full-stack-fastapi-postgresql/tree/master/%7B%7Bcookiecutter.project_slug%7D%7D/backend might also need an update. Let me know if you'd like me to open a PR.

[tiangolo]

Thanks for the interest! 🍰

Now that Uvicorn supports managing workers with --workers, including restarting dead ones, there's no need for Gunicorn. That also means that it's much simpler to build a Docker image from scratch now, I updated the docs to explain it.

Because of that, I deprecated this Docker image: https://github.com/tiangolo/uvicorn-gunicorn-docker#-warning-you-probably-dont-need-this-docker-image

Given that, I'll now close this one, but thanks for the effort! ☕