[MM-16389] Add icon_emoji parameter to webhooks (#11586)

[MM-16389] Add icon_emoji field to posts from incoming webhooks

To be used to substitute the profile picture on posts.

model/emoji.go

@@ -31,6 +31,11 @@ func inSystemEmoji(emojiName string) bool {
 	return ok
 }
 
+func GetSystemEmojiId(emojiName string) (string, bool) {
+	id, found := SystemEmojis[emojiName]
+	return id, found
+}
+
 func (emoji *Emoji) IsValid() *AppError {
 	if len(emoji.Id) != 26 {
 		return NewAppError("Emoji.IsValid", "model.emoji.id.app_error", nil, "", http.StatusBadRequest)

model/incoming_webhook.go

@@ -38,6 +38,7 @@ type IncomingWebhookRequest struct {
 	Props       StringInterface    `json:"props"`
 	Attachments []*SlackAttachment `json:"attachments"`
 	Type        string             `json:"type"`
+	IconEmoji   string             `json:"icon_emoji"`
 }
 
 func (o *IncomingWebhook) ToJson() string {

model/post.go

@@ -50,8 +50,11 @@ const (
 	POST_CUSTOM_TYPE_PREFIX     = "custom_"
 	POST_ME                     = "me"
 	PROPS_ADD_CHANNEL_MEMBER    = "add_channel_member"
-	POST_PROPS_ADDED_USER_ID    = "addedUserId"
-	POST_PROPS_DELETE_BY        = "deleteBy"
+
+	POST_PROPS_ADDED_USER_ID       = "addedUserId"
+	POST_PROPS_DELETE_BY           = "deleteBy"
+	POST_PROPS_OVERRIDE_ICON_URL   = "override_icon_url"
+	POST_PROPS_OVERRIDE_ICON_EMOJI = "override_icon_emoji"
 )
 
 type Post struct {