Support configuring retry policy when registering a function in v4

[ejizba]

Example function.json from v3

{
    "bindings": [
        {
            ....
        }
    ],
    "retry": {
        "strategy": "fixedDelay",
        "maxRetryCount": 4,
        "delayInterval": "00:00:10"
    }
}

We don't have an analogous place for people to put the "retry" properties in v4.