Guide to using an external Postgres backend

[scottmas]

For political reasons and safety reasons, my employer won't even consider letting me use EdgeDB unless we have a very easy escape hatch to the underlying Postgres instance.

However, it is a nightmare right now trying to figure out how to adopt EdgeDB while using our own external instance. There's next to no documentation on the --backend-dsn flag and the specifics of it all.

A guide would be amazing.