MEDIUM: cli: Add payload support

In order to use arbitrary data in the CLI (multiple lines or group of words
that must be considered as a whole, for example), it is now possible to add a
payload to the commands. To do so, the first line needs to end with a special
pattern: <<\n. Everything that follows will be left untouched by the CLI parser
and will be passed to the commands parsers.

Per-command support will need to be added to take advantage of this
feature.

Signed-off-by: Aurélien Nephtali <aurelien.nephtali@corp.ovh.com>
diff --git a/src/cache.c b/src/cache.c
index 39e0bad..c72d9de 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -952,7 +952,7 @@
 
 };
 
-static int cli_parse_show_cache(char **args, struct appctx *appctx, void *private)
+static int cli_parse_show_cache(char **args, char *payload, struct appctx *appctx, void *private)
 {
 	if (!cli_has_level(appctx, ACCESS_LVL_ADMIN))
 		return 1;