CLEANUP: vars: name the temporary proxy "CFG" instead of "CLI" for global vars

We're using a dummy temporary proxy when creating global variables in
the configuration file, it was copied from the CLI's code and was
mistakenly called "CLI", better name it "CFG". It should not appear
anywhere except maybe when debugging cores.

src/vars.c

@@ -902,7 +902,7 @@ static int vars_parse_global_set_var(char **args, int section_type, struct proxy
                                      char **err)
 {
 	struct proxy px = {
-		.id = "CLI",
+		.id = "CFG",
 		.conf.args.file = file,
 		.conf.args.line = line,
 	};