Add support for Go Appengine SDK

[yohcop]

It probably wouldn't be too different from python.

[rodrigoaliste]

Any updates?

[pmbethe09]

as far as I know, there is no active work on this feature.

[ccontavalli]

In case anyone is looking into this:

• flex environment is easy, create container, and push container.
• for the standard environment... https://github.com/ccontavalli/bazel-rules/tree/master/appengine is ugly but works.