Add createdAt property to Signature Request object

[janetanne]

When using GetSignatureRequest(), there is currently no createdAt property in the response that is parallel to created_at in the API response.

If you look at the BaseSignatureRequest model you can confirm this: https://github.com/hellosign/hellosign-dotnet-sdk/blob/v3/src/HelloSign/Models/BaseSignatureRequest.cs

The workaround would be to make a raw HTTP request to the endpoint as we have more parameters available in the API vs. the C# SDK.

Internal reference number: 10071 // 11796
Related ticket number: 11001942

[mattoosterbaan]

I have a pull request out there that takes care of this: PR #88