MINOR: http: add a new "replace-path" action

This action is very similar to "replace-uri" except that it only acts on the
path component. This is assumed to better match users' expectations when they
used to rely on "replace-uri" in HTTP/1 because mostly origin forms were used
in H1 while mostly absolute URI form is used in H2, and their rules very often
start with a '/', and as such do not match.

It could help users to get this backported to 2.0 and 2.1.
diff --git a/src/cfgparse-listen.c b/src/cfgparse-listen.c
index 507e071..9975e46 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -3694,7 +3694,7 @@
 	}
 	else if (!strcmp(args[0], "cliexp") || !strcmp(args[0], "reqrep")) {  /* replace request header from a regex */
 		ha_alert("parsing [%s:%d] : The '%s' directive is not supported anymore since HAProxy 2.1. "
-			 "Use 'http-request replace-uri' and 'http-request replace-header' instead.\n",
+			 "Use 'http-request replace-path', 'http-request replace-uri' or 'http-request replace-header' instead.\n",
 			 file, linenum, args[0]);
 		err_code |= ERR_ALERT | ERR_FATAL;
 		goto out;