How would I connect an external tool such as dbeaver / datagrip / … to my database ?
This is fully supported as long as your application supports connecting over an SSH tunnel. More details here
To summarize: connect with your ssh username, typically <project id>-<branch>-<hash>--<app> to your ssh.<region>.platform.sh. From there, your database host will be for example database.internal and your credentials are user and an empty password, if you haven’t modified your db service before.
Another way is using platform tunnel to create tunnels to your services and then accessing them via a localhost:port combination. This is spelled out in more detail in our Docs as well.