switch to redis pubsub for ipc

adjust commands to utilize channel names
add new config variables
fix mention race condition

default.yaml

@@ -1067,3 +1067,9 @@ history:
 # whether to allow customization of the config at runtime using environment variables,
 # e.g., ERGO__SERVER__MAX_SENDQ=128k. see the manual for more details.
 allow-environment-overrides: true
+
+cef:
+    imagor:
+        url: "https://example.com/embed/"
+        secret: "secretgoeshere"
+    redis: "redis://user:password@localhost:6379/0?protocol=3"