[MM-9938] Add support for multiple responses from a slash command (#9836)

* slash command response now supports multiple posts

* change wording of Posts to ExtraResponses

model/command_response.go

@@ -18,14 +18,15 @@ const (
 )
 
 type CommandResponse struct {
-	ResponseType string             `json:"response_type"`
-	Text         string             `json:"text"`
-	Username     string             `json:"username"`
-	IconURL      string             `json:"icon_url"`
-	Type         string             `json:"type"`
-	Props        StringInterface    `json:"props"`
-	GotoLocation string             `json:"goto_location"`
-	Attachments  []*SlackAttachment `json:"attachments"`
+	ResponseType   string             `json:"response_type"`
+	Text           string             `json:"text"`
+	Username       string             `json:"username"`
+	IconURL        string             `json:"icon_url"`
+	Type           string             `json:"type"`
+	Props          StringInterface    `json:"props"`
+	GotoLocation   string             `json:"goto_location"`
+	Attachments    []*SlackAttachment `json:"attachments"`
+	ExtraResponses []*CommandResponse `json:"extra_responses"`
 }
 
 func (o *CommandResponse) ToJson() string {
@@ -63,5 +64,11 @@ func CommandResponseFromJson(data io.Reader) (*CommandResponse, error) {
 
 	o.Attachments = StringifySlackFieldValue(o.Attachments)
 
+	if o.ExtraResponses != nil {
+		for _, resp := range o.ExtraResponses {
+			resp.Attachments = StringifySlackFieldValue(resp.Attachments)
+		}
+	}
+
 	return &o, nil
 }