[invoke/verifyState] Add optional `accountLinkingUrl` return type for invoke

[aacebo]

To support a change in the Teams FE, we need to optionally allow developers to configure a static account linking url that, if present, would be returned to the Teams Platform after processing of the activity.

Platform Code:
https://skype.visualstudio.com/SCC/_git/async_messaging_botapiservice/pullrequest/1264762?_a=files#:~:text=var%20obj%20%3D%20JToken,string)obj%3F%5B%22accountLinkingUrl%22%5D%3B