TeamsAgentExtension: OnConversationUpdate: Typed handlers

[tracyboehrer]

The Teams OnConversationUpdate handler will require the dev to extract relevant information from Activity.ChannelData. This is a reduction in functionality from TeamsActivityHandler.

Some consideration should be given to different handler delegates, perhaps generic to allow at least the TeamsChannelData, if not the specific objects provided in the equivalent TeamsActivityHandler methods (ChannelInfo or TeamInfo).

[tracyboehrer]

@Rido For visibility since you raised the issue in conversation.