fix (events): convert multierror to stdlib error (#3743)

* fix (events): convert multierror to stdlib error

multierror errors will be converted to a stdlib error (because
multierror doesn't support json marshaling).

* refact (errors): convert from multierror to stdlib errors.Join(...)

* refact: convert from pkg/errors to stdlib error wrapping

go.mod

@@ -63,7 +63,7 @@ require (
 	github.com/oligot/go-mod-upgrade v0.9.1
 	github.com/ory/dockertest/v3 v3.9.1
 	github.com/pires/go-proxyproto v0.7.0
-	github.com/pkg/errors v0.9.1
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/posener/complete v1.2.3
 	github.com/prometheus/client_golang v1.12.1
 	github.com/ryanuber/go-glob v1.0.0