Set EndOfConversationCodes when send EoC

[xieofxie]

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Is your feature request related to a problem? Please describe.
Currently when sending EoC here https://github.com/microsoft/botbuilder-dotnet/blob/master/libraries/Microsoft.Bot.Builder.Dialogs/DialogExtensions.cs#L91, Code is not set to any of the EndOfConversationCodes https://github.com/microsoft/botbuilder-dotnet/blob/master/libraries/Microsoft.Bot.Schema/EndOfConversationCodes.cs

Describe the solution you'd like
Set to CompletedSuccessfully

Describe alternatives you've considered

Additional context

[enhancement]

[mrivera-ms]

Probably a protocol change. Likely channel specific. It is unclear how to handle it.

[EricDahlvang]

Couldn't we just convert the dialog Status into the corresponding EndOfConversationCode?

DialogTurnStatus.Complete == EndOfConversationCodes.CompletedSuccessfully 
DialogTurnStatus.Cancelled == EndOfConversationCodes.UserCancelled 

[cleemullins]

@EricDahlvang IS this something we should take in R10, or push to R11?

[EricDahlvang]

@cleemullins Seems like a small change. I should be able to get it into R10.