MDEV-21375: Get option group suffix from $MARIADB_GROUP_SUFFIX in addition to $MYSQL_GROUP_SUFFIX

Add check for MARIADB_GROUP_SUFFIX environment variable when
--default-group-suffix argument is not passed. This environment variable
will take precedence over the MYSQL_GROUP_SUFFIX environment variable if
both are set.

All new code of the whole pull request, including one or several files that are
either new files or modified ones, are contributed under the BSD-new license. I
am contributing on behalf of my employer Amazon Web Services, Inc.

Author: amarjilani

mysys/my_default.c

@@ -317,6 +317,9 @@ int get_defaults_options(char **argv)
     argv++;
   }
 
+  if (! my_defaults_group_suffix)
+    my_defaults_group_suffix= getenv("MARIADB_GROUP_SUFFIX");
+
   if (! my_defaults_group_suffix)
     my_defaults_group_suffix= getenv("MYSQL_GROUP_SUFFIX");