Greeting isn't greeting

[clearab]

In all our generators we use the mis-labelled "Greeting" trigger to trigger our welcome/greeting dialogs. Unfortunately, this isn't actually a Greeting trigger, it fires on all ConversationUpdate Activities (which includes a lot more than membersAdded events). We need to add testing of the type of ConversationUpdate to all of these, and only do the greeting for the membersAdded type.

[clearab]

Related: https://github.com/microsoft/BotFramework-Composer/issues/7033

[ryanisgrig]

See also:

• microsoft/botframework-components#939
• microsoft/botbuilder-dotnet#5502