Document new velocity system properties

Author: Warriorrrr

src/content/docs/velocity/admin/reference/system-properties.md

@@ -115,6 +115,15 @@ The default value shown may not be set for the property but will only be used by
 - **default**: `true`
 - **description**: Whether the client should disconnect on packet errors. Temporarily added in MC 1.20.5 and removed in 1.21.2 to help modded servers transition to this change.
 
+#### velocity.maximum-play-queue-size
+
+- **default**: `134217728` (128 MiB)
+- **description**: The maximum size of the queue (in bytes) that holds pending PLAY state packets sent to the client while it is in the CONFIG state.
+
+#### velocity.max-plugin-message-payload-size
+- **default**: `32767`
+- **description**: The maximum allowed size of plugin message packets in bytes.
+
 ## List of environment variables
 
 #### VELOCITY_FORWARDING_SECRET