Cosmos DB items with datetime as string that has time zone offset loses time zone

Due to this well-known bug in Json.NET: https://github.com/JamesNK/Newtonsoft.Json/issues/525

To get around this bad default, the C# users can override the settings here: https://github.com/Azure/azure-webjobs-sdk-extensions/pull/575

Unfortunately, this is **not** a viable option for non-.NET languages. We need to introduce some sort of way for time zones to be preserved and set:
```csharp
JsonConvert.DefaultSettings = () => new JsonSerializerSettings
{
DateParseHandling = DateParseHandling.None
};
```