Shortcake should more gracefully handle not being able find database

[BryceBeagle]

Right now it crashes:

Traceback (most recent call last):
  File "/shortcake/main.py", line 28, in <module>
    main()
  File "/shortcake/main.py", line 16, in main
    if not database.exists:
  File "/shortcake/shortcake/database/management.py", line 41, in exists
    return sqlalchemy_utils.database_exists(self.uri)
  File "/venv/lib/python3.9/site-packages/sqlalchemy_utils/functions/database.py", line 466, in database_exists
    return bool(get_scalar_result(engine, text))
  File "/venv/lib/python3.9/site-packages/sqlalchemy_utils/functions/database.py", line 445, in get_scalar_result
    result_proxy = engine.execute(sql)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/engine/base.py", line 2234, in execute
    connection = self._contextual_connect(close_with_result=True)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/engine/base.py", line 2302, in _contextual_connect
    self._wrap_pool_connect(self.pool.connect, None),
  File "/venv/lib/python3.9/site-packages/sqlalchemy/engine/base.py", line 2339, in _wrap_pool_connect
    Connection._handle_dbapi_exception_noconnection(
  File "/venv/lib/python3.9/site-packages/sqlalchemy/engine/base.py", line 1583, in _handle_dbapi_exception_noconnection
    util.raise_(
  File "/venv/lib/python3.9/site-packages/sqlalchemy/util/compat.py", line 182, in raise_
    raise exception
  File "/venv/lib/python3.9/site-packages/sqlalchemy/engine/base.py", line 2336, in _wrap_pool_connect
    return fn()
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/base.py", line 364, in connect
    return _ConnectionFairy._checkout(self)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/base.py", line 778, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/base.py", line 495, in checkout
    rec = pool._do_get()
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/impl.py", line 140, in _do_get
    self._dec_overflow()
  File "/venv/lib/python3.9/site-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
    compat.raise_(
  File "/venv/lib/python3.9/site-packages/sqlalchemy/util/compat.py", line 182, in raise_
    raise exception
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/impl.py", line 137, in _do_get
    return self._create_connection()
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/base.py", line 309, in _create_connection
    return _ConnectionRecord(self)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/base.py", line 440, in __init__
    self.__connect(first_connect_check=True)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/base.py", line 661, in __connect
    pool.logger.debug("Error on connect(): %s", e)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
    compat.raise_(
  File "/venv/lib/python3.9/site-packages/sqlalchemy/util/compat.py", line 182, in raise_
    raise exception
  File "/venv/lib/python3.9/site-packages/sqlalchemy/pool/base.py", line 656, in __connect
    connection = pool._invoke_creator(self)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/engine/strategies.py", line 114, in connect
    return dialect.connect(*cargs, **cparams)
  File "/venv/lib/python3.9/site-packages/sqlalchemy/engine/default.py", line 508, in connect
    return self.dbapi.connect(*cargs, **cparams)
  File "/venv/lib/python3.9/site-packages/psycopg2/__init__.py", line 127, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) could not translate host name "postgres" to address: Name does not resolve