MM-42927: Use new gosaml2 library (#20004)

```release-note
NONE
```

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

go.mod

@@ -63,7 +63,7 @@ require (
 	github.com/lib/pq v1.10.4
 	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/mattermost/go-i18n v1.11.1-0.20211013152124-5c415071e404
-	github.com/mattermost/gosaml2 v0.3.3
+	github.com/mattermost/gosaml2 v0.8.0
 	github.com/mattermost/gziphandler v0.0.1
 	github.com/mattermost/ldap v0.0.0-20201202150706-ee0e6284187d
 	github.com/mattermost/logr/v2 v2.0.15