SMTP: Support SASL XOAUTH2

Signed-off-by: Jan-Otto Kröpke <[email protected]>

Author: jkroepke

go.mod

@@ -10,6 +10,7 @@ require (
 	github.com/cenkalti/backoff/v4 v4.3.0
 	github.com/cespare/xxhash/v2 v2.3.0
 	github.com/coder/quartz v0.1.2
+	github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21 // indirect
 	github.com/emersion/go-smtp v0.21.3
 	github.com/go-openapi/analysis v0.23.0
 	github.com/go-openapi/errors v0.22.0
@@ -60,7 +61,6 @@ require (
 	github.com/coreos/go-systemd/v22 v22.5.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
-	github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21 // indirect
 	github.com/go-logr/logr v1.4.1 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-openapi/jsonpointer v0.21.0 // indirect