Enable pprof endpoints on metrics server

This follows the suggestion from the controller-runtime library to use
the `AddMetricsExtraHandler`.

Signed-off-by: Hidde Beydals <hello@hidde.co>

Author: hiddeco

go.mod

@@ -12,7 +12,7 @@ require (
 	github.com/fluxcd/pkg/gittestserver v0.1.0
 	github.com/fluxcd/pkg/helmtestserver v0.1.0
 	github.com/fluxcd/pkg/lockedfile v0.0.5
-	github.com/fluxcd/pkg/runtime v0.8.0
+	github.com/fluxcd/pkg/runtime v0.8.1-0.20210206225502-5c2370b71e43
 	github.com/fluxcd/pkg/ssh v0.0.5
 	github.com/fluxcd/pkg/untar v0.0.5
 	github.com/fluxcd/pkg/version v0.0.1