do not add save parameter during config rewrite in sentinel mode (#7945)

Previous code would have added default redis save parameters
to the config file on rewrite, which would have been silently ignored
when the config file is loaded.

The new code avoids adding this, and also actively removes these lines
If added by a previous config rewrite. 

(cherry picked from commit 0f370f9)

src/config.c

@@ -1323,6 +1323,12 @@ void rewriteConfigSaveOption(struct rewriteConfigState *state) {
     int j;
     sds line;
 
+    /* In Sentinel mode we don't need to rewrite the save parameters */
+    if (server.sentinel_mode) {
+        rewriteConfigMarkAsProcessed(state,"save");
+        return;
+    }
+
     /* Note that if there are no save parameters at all, all the current
      * config line with "save" will be detected as orphaned and deleted,
      * resulting into no RDB persistence as expected. */