metrics_exporter: merge router metrics into /metrics output

Include router context counters in metrics export.
Enable routing metrics scraping without additional config.

Signed-off-by: Eduardo Silva <eduardo@chronosphere.io>

Author: edsiper

src/flb_metrics_exporter.c

@@ -34,6 +34,7 @@
 #include <fluent-bit/flb_storage.h>
 #include <fluent-bit/flb_metrics.h>
 #include <fluent-bit/flb_metrics_exporter.h>
+#include <fluent-bit/flb_router.h>
 
 static int collect_inputs(msgpack_sbuffer *mp_sbuf, msgpack_packer *mp_pck,
                           struct flb_config *ctx)
@@ -308,6 +309,15 @@ struct cmt *flb_me_get_cmetrics(struct flb_config *ctx)
         }
     }
 
+    if (ctx->router && ctx->router->cmt) {
+        ret = cmt_cat(cmt, ctx->router->cmt);
+        if (ret == -1) {
+            flb_error("[metrics exporter] could not append routing metrics");
+            cmt_destroy(cmt);
+            return NULL;
+        }
+    }
+
     /* Pipeline metrics: input, filters, outputs */
     mk_list_foreach(head, &ctx->inputs) {
         i = mk_list_entry(head, struct flb_input_instance, _head);