chore(config): upgrade to gosettings v0.4.0

- drop qdm12/govalid dependency
- upgrade qdm12/ss-server to v0.6.0
- do not unset sensitive config settings (makes no sense to me)

internal/configuration/sources/secrets/interfaces.go

@@ -0,0 +1,5 @@
+package secrets
+
+type Warner interface {
+	Warnf(format string, a ...interface{})
+}