feat(oohelperd): measure TLS for :443 endpoints (#886)

This diff improves oohelperd to measure :443 endpoints with TLS.

Part of https://github.com/ooni/probe/issues/2237.

internal/cmd/oohelperd/handler.go

@@ -29,6 +29,9 @@ type handler struct {
 
 	// NewResolver is the MANDATORY factory for creating a new resolver.
 	NewResolver func() model.Resolver
+
+	// NewTLSHandshaker is the MANDATORY factory for creating a new TLS handshaker.
+	NewTLSHandshaker func() model.TLSHandshaker
 }
 
 var _ http.Handler = &handler{}