Correctly describe the meaning of unspecified rule lists in the [`alias_creation_rules`](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#alias_creation_rules) and [`room_list_publication_rules`](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#room_list_publication_rules) config options and improve their descriptions more generally.