[lakebox] Default staging SSH gateway to ue1.s.dbrx.dev

us-east-1 is the staging region where the SSH gateway is reachable in
practice; uw2.s.dbrx.dev does not have a routable lakebox listener.
Users targeting a different staging region can still override with
--gateway.

Co-authored-by: Isaac

Author: shuochen0311

cmd/lakebox/ssh.go

@@ -16,7 +16,7 @@ import (
 
 const (
 	defaultGatewayHost        = "uw2.dbrx.dev"
-	stagingDefaultGatewayHost = "uw2.s.dbrx.dev"
+	stagingDefaultGatewayHost = "ue1.s.dbrx.dev"
 	defaultGatewayPort        = "2222"
 )