template: Github actions starter action

[ascott18]

• A build action, and a release/deployment action (that deploys to a theoretical azure app service)
• Deployment should be reasonably explained/obvious how to scale to multiple environments
• Add this behind a new template parameter (in template.json)
• Don't include dependency caching. In my observed experience this actually makes the build slower. And its just more "stuff" for someone to have to grok.