register federation failure metrics (#7081)

Closes gh-7080

Signed-off-by: Julian Taylor <juliantaylor108@gmail.com>

web/federate.go

@@ -44,6 +44,10 @@ var (
 	})
 )
 
+func registerFederationMetrics(r prometheus.Registerer) {
+	r.MustRegister(federationWarnings, federationErrors)
+}
+
 func (h *Handler) federation(w http.ResponseWriter, req *http.Request) {
 	h.mtx.RLock()
 	defer h.mtx.RUnlock()

web/web.go

@@ -139,6 +139,7 @@ func newMetrics(r prometheus.Registerer) *metrics {
 
 	if r != nil {
 		r.MustRegister(m.requestCounter, m.requestDuration, m.responseSize)
+		registerFederationMetrics(r)
 	}
 	return m
 }