MINOR: uri_normalizer: Add http-request normalize-uri

This patch adds the `http-request normalize-uri` action that was requested in
GitHub issue #714.

Normalizers will be added in the next patches.

include/haproxy/action-t.h

@@ -101,6 +101,10 @@ enum act_timeout_name {
 	ACT_TIMEOUT_TUNNEL,
 };
 
+enum act_normalize_uri {
+	ACT_NORMALIZE_URI_PLACEHOLDER,
+};
+
 /* NOTE: if <.action_ptr> is defined, the referenced function will always be
  *       called regardless the action type. */
 struct act_rule {