Update SkillHttpClient/BotFrameworkClient to support audience and bufferedReplies #799
Description
Describe the bug
The SkillHttpClient needs to include an overload that takes an audience and passes it through to the SkillConversationIdFactory for storage.
This audience is required so that when the SkillConversationIdFactory is used via the SkillHandler class, the correct ConnectorClient is created for sending activities.
We need another method to enable configuring "bufferedReplies" on Activity.DeliveryMode for forwarded activities.
Additional context
waiting on #780
PR microsoft/botbuilder-dotnet#3409 that added ContinueConversationAsync overload to require audience.