Add an API Endpoint /getVersion

[madhavajay]

This will send a header with the current version.
Additionally the logic will either send a status ok, or an upgrade command.

Later we can add code to check the user-agent and version etc.

For now just short circuit to upgrade command so we can integrate / test this in the app code bases.
Ok command:
Custom Header:
"X-API-Version": {{current version}}

{
    "status": "200",
    "message": "App version ok"
}

Upgrade command:
Custom Header:
"X-API-Version": {{current version}}

{
    "status": "426",
    "message": "Please upgrade your client"
}

[zssz]

X-API-Version header for specifying the version the client is expecting. Great!