SQLALCHEMY_DATABASE_URI with `sqlite:////...` with the full path to the data/webpush.db file.
(Why does the relative path of `sqlite:///...` not work for a relative path?)
* Another potential problem with "unable to open database file" is the permissions on the directory or file with the DB, as set on the local volume that matches the docker `/app/instance/data` directory. Note that the user id in the Dockerfile is set to 1000; the `id` command will tell you the uid for your user, which should match.
* Another potential problem with "unable to open database file" is the
permissions on the directory or file with the DB, as set on the local volume
that matches the docker `/app/instance/data` directory. Note that the user id
in the Dockerfile is set to 1000; the `id` command will tell you the uid for
your user, which should match. Then, user with uid 1000 should have write
permissions to both the file and the directory, and have execute permissions
