Add Prometheus metrics

Closes #197

Co-authored-by: haywo <haywo@nct08.de>

go.mod

@@ -15,7 +15,8 @@ require (
 	gopkg.in/yaml.v2 v2.3.0
 	maunium.net/go/mauflag v1.0.0
 	maunium.net/go/maulogger/v2 v2.1.1
-	maunium.net/go/mautrix v0.5.0
+	maunium.net/go/mautrix v0.5.1
+	github.com/prometheus/client_golang v1.6.0
 )
 
-replace github.com/Rhymen/go-whatsapp => github.com/tulir/go-whatsapp v0.2.8
+replace github.com/Rhymen/go-whatsapp => github.com/tulir/go-whatsapp v0.3.0