MINOR: stick-table: add sc-add-gpc() to http-after-response

sc-add-gpc() was implemented in 5a72d03 ("MINOR: stick-table:
implement the sc-add-gpc() action")

This new action was exposed everywhere sc-inc-gpc() is available,
except for http-after-response.
But there doesn't seem to be a technical constraint that prevents us from
exposing it in http-after-response.
It was probably overlooked, let's add it.

No backport needed, unless 5a72d03 ("MINOR: stick-table: implement the
sc-add-gpc() action") is being backported.
diff --git a/src/stick_table.c b/src/stick_table.c
index de40f41..d748705 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -5326,6 +5326,7 @@
 INITCALL1(STG_REGISTER, http_res_keywords_register, &http_res_kws);
 
 static struct action_kw_list http_after_res_kws = { { }, {
+	{ "sc-add-gpc",  parse_add_gpc,  KWF_MATCH_PREFIX },
 	{ "sc-inc-gpc",  parse_inc_gpc,  KWF_MATCH_PREFIX },
 	{ "sc-inc-gpc0", parse_inc_gpc,  KWF_MATCH_PREFIX },
 	{ "sc-inc-gpc1", parse_inc_gpc,  KWF_MATCH_PREFIX },