[App Service] sample web app deployed automatically from GitHub

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## This issue is a: (mark with an `x`)

- [ ] bug report
- [x] request for new sample
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)

## Steps to reproduce:

## Errors and log messages:

## Expected behavior:
Provide sample about how to use source control as deployment option for web app.

## OS and Go versions:

## Further info: