add missing yamls in controllers/nginx

[harryge00]

examples/ingress.yaml and examples/default/rc-default.yaml are missing. And I did not find the latter...

Add default-backend.yaml because it is used.

[k8s-ci-robot]

Thanks for your pull request. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please follow instructions at https://github.com/kubernetes/kubernetes/wiki/CLA-FAQ to sign the CLA.

It may take a couple minutes for the CLA signature to be fully registered; after that, please reply here with a new comment and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please sign in with your organization's credentials at https://identity.linuxfoundation.org/projects/cncf to be authorized.
• If you have done the above and are still having issues with the CLA being reported as unsigned, please email the CNCF helpdesk: helpdesk@rt.linuxfoundation.org

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[k8s-reviewable]

This change is 

[coveralls]

Coverage remained the same at 43.613% when pulling 4e1ae0efb7bae2d20b1cfca20d518697fb486419 on harryge00:add-yaml-to-nginx-controller into 2d6f811 on kubernetes:master.

[coveralls]

Coverage remained the same at 43.613% when pulling 4e1ae0efb7bae2d20b1cfca20d518697fb486419 on harryge00:add-yaml-to-nginx-controller into 2d6f811 on kubernetes:master.

[coveralls]

Coverage decreased (-0.02%) to 43.588% when pulling 6dd1b0b on harryge00:add-yaml-to-nginx-controller into 2d6f811 on kubernetes:master.

[aledbf]

@harryge00 thanks!