feat!: the general.secret_key configuration field is now required (#2841)

BREAKING CHANGE: The `general.secret_key` configuration field is now
required. Make sure to update your configuration file and add a secret
key.

Closes #2426

playout/tests/liquidsoap/fixtures/__init__.py

@@ -9,6 +9,7 @@ def make_config(**kwargs) -> Config:
             "general": {
                 "public_url": "http://localhost:8080",
                 "api_key": "some_api_key",
+                "secret_key": "some_secret_key",
             },
             **kwargs,
         }