BUG/MINOR: promex: Set conn-stream/channel EOI flags at the end of request

This bug is the same than for the HTTP client. See "BUG/MINOR: httpclient:
Set conn-stream/channel EOI flags at the end of request" for details.

This patch must be backported as far as 2.0. But only CF_EOI must be set
because applets are not attached to a conn-stream on older versions.
diff --git a/addons/promex/service-prometheus.c b/addons/promex/service-prometheus.c
index 5158d32..06eb1ee 100644
--- a/addons/promex/service-prometheus.c
+++ b/addons/promex/service-prometheus.c
@@ -1511,6 +1511,8 @@
 		case PROMEX_ST_DONE:
 			/* no more data are expected. Don't add TLR because mux-h1 will take care of it */
 			res_htx->flags |= HTX_FL_EOM;
+			si->cs->flags |= CS_FL_EOI;
+			res->flags |= CF_EOI;
 			appctx->st0 = PROMEX_ST_END;
 			/* fall through */