chore(tests) add namespace to test deployments

[jpeach]

Summary

Add the namespace resource to the external service deployment YAML so
that it can be applied as a single step without any manual prerequisites.

Full changelog

N/A

Issues resolved

N/A

Documentation

N/A

Testing

$ k get ns
NAME                 STATUS   AGE
default              Active   2d18h
kube-node-lease      Active   2d18h
kube-public          Active   2d18h
kube-system          Active   2d18h
kuma-system          Active   2d17h
local-path-storage   Active   2d18h

$ k apply -f test/e2e/externalservices/testdata/externalservice-http-server.yaml
namespace/externalservice-namespace created
service/externalservice-http-server created
deployment.apps/externalservice-http-server created

$ k apply -f test/e2e/externalservices/testdata/externalservice-https-server.yaml
namespace/externalservice-namespace unchanged
service/externalservice-https-server created
deployment.apps/externalservice-https-server created

[bartsmykla]

lgtm