Add new endpoint for aker version

[schmidtw]

/aker/service/version/upstream should return the github repo commit hash in msgpack format like:

{
    "upstream": "8c310fcae2a35fd1dc139584ce9d5b289736e1a8"
}

[manderiasian]

Will we be adding a "service/..." to Aker in git? There is nothing there now.

[schmidtw]

We need to add the service/version/upstream endpoint in git. The extra path elements are for future growth.