Add functionality to update serializer settings to fix datetime parsing issue

[surgupta-msft]

Resolves - Azure/azure-functions-dotnet-worker#2442

Users can provide configuration for cosmosDB extension via Host.json - docs

{
    "version": "2.0",
    "extensions": {
        "cosmosDB": {
            "serializerSettings": {
              "dateParseHandling":  "None"
            }
        }
    }
}