[Nginx] prometheus scrape annotations

[dannyk81]

This PR adds to the nginx DaemonSet and Deployment examples annotations that are required for Prometheus automatic discovery and scraping of the nginx ingress controller /metrics endpoint.

This fixed #464

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[k8s-reviewable]

This change is 

[dannyk81]

I signed it!

[aledbf]

@dannyk81 please squash the commits

[coveralls]

Coverage remained the same at 43.146% when pulling 97c4687 on dannyk81:nginx/prometheus-scrape-annotations into 62070a1 on kubernetes:master.

[dannyk81]

@aledbf done, sorry about that 👍

[aledbf]

/lgtm

[coveralls]

Coverage remained the same at 43.146% when pulling 6a38a1a on dannyk81:nginx/prometheus-scrape-annotations into 62070a1 on kubernetes:master.

[aledbf]

@dannyk81 thanks!

[dannyk81]

My pleasure 😊

Thanks for merging this.