redis.conf: Add data loss warning to "appendonly" (redis#12506)

warning against editing the config file and restarting the server.
which will attempt to load an AOF file and disregard the RDB.

Co-authored-by: Oran Agra <oran@redislabs.com>

redis.conf

@@ -1382,6 +1382,10 @@ disable-thp yes
 # If the AOF is enabled on startup Redis will load the AOF, that is the file
 # with the better durability guarantees.
 #
+# Note that changing this value in a config file of an existing database and
+# restarting the server can lead to data loss. A conversion needs to be done
+# by setting it via CONFIG command on a live server first.
+#
 # Please check https://redis.io/topics/persistence for more information.
 
 appendonly no