fix: Use shallow mode when cloning submodules (#1253)

.gitmodules

@@ -2,27 +2,34 @@
 	path = istio/api
 	url = https://github.com/higress-group/api
 	branch = istio-1.19
+	shallow = true
 [submodule "istio/istio"]
 	path = istio/istio
 	url = https://github.com/higress-group/istio
 	branch = istio-1.19
+	shallow = true
 [submodule "istio/client-go"]
 	path = istio/client-go
 	url = https://github.com/higress-group/client-go
 	branch = istio-1.19
+	shallow = true
 [submodule "istio/pkg"]
 	path = istio/pkg
 	url = https://github.com/higress-group/pkg
 	branch = istio-1.19
+	shallow = true
 [submodule "istio/proxy"]
 	path = istio/proxy
 	url = https://github.com/higress-group/proxy
-        branch = istio-1.19
+	branch = istio-1.19
+	shallow = true
 [submodule "envoy/go-control-plane"]
 	path = envoy/go-control-plane
 	url = https://github.com/higress-group/go-control-plane
-        branch = istio-1.19
+	branch = istio-1.19
+	shallow = true
 [submodule "envoy/envoy"]
 	path = envoy/envoy
 	url = https://github.com/higress-group/envoy
-        branch = envoy-1.27
+	branch = envoy-1.27
+	shallow = true