Add ephemeral response_type to the Slack connector IneractiveAction r…

…espond method

- Added in kwargs to the respond method
- Set response_type variable based on kwarg with same name
- Set response_type based on value passed in for the case where
  response_event is a str

opsdroid/connector/slack/events.py

@@ -69,8 +69,9 @@ def __init__(self, payload, *args, **kwargs):
         self.payload = payload
         self.ssl_context = ssl.create_default_context(cafile=certifi.where())
 
-    async def respond(self, response_event):
+    async def respond(self, response_event, **kwargs):
         """Respond to this message using the response_url field in the payload."""
+        response_type = kwargs.get("response_type", "in_channel")
 
         if isinstance(response_event, str):
             if "response_url" in self.payload:
@@ -83,7 +84,7 @@ async def respond(self, response_event):
                                 "text": response_event,
                                 "replace_original": False,
                                 "delete_original": False,
-                                "response_type": "in_channel",
+                                "response_type": response_type,
                             }
                         ),
                         headers=headers,