Create example_github_action.yml

[patmmccann]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Example

• What is the current behavior? (You can also link to an open issue here)
  no github action easy to author

• What is the new behavior (if this is a feature change)?
  github action simple to deploy

• Other information:
  in production use at prebid.js

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This change is 

[kucherenko]

@patmmccann thank you, merged