[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.

app/webhook.go

@@ -138,7 +138,7 @@ func (a *App) TriggerWebhook(payload *model.OutgoingWebhookPayload, hook *model.
 				if *a.Config().ServiceSettings.EnablePostIconOverride && hook.IconURL != "" && webhookResp.IconURL == "" {
 					webhookResp.IconURL = hook.IconURL
 				}
-				if _, err := a.CreateWebhookPost(hook.CreatorId, channel, text, webhookResp.Username, webhookResp.IconURL, webhookResp.Props, webhookResp.Type, postRootId); err != nil {
+				if _, err := a.CreateWebhookPost(hook.CreatorId, channel, text, webhookResp.Username, webhookResp.IconURL, "", webhookResp.Props, webhookResp.Type, postRootId); err != nil {
 					mlog.Error(fmt.Sprintf("Failed to create response post, err=%v", err))
 				}
 			}
@@ -245,7 +245,7 @@ func SplitWebhookPost(post *model.Post, maxPostSize int) ([]*model.Post, *model.
 	return splits, nil
 }
 
-func (a *App) CreateWebhookPost(userId string, channel *model.Channel, text, overrideUsername, overrideIconUrl string, props model.StringInterface, postType string, postRootId string) (*model.Post, *model.AppError) {
+func (a *App) CreateWebhookPost(userId string, channel *model.Channel, text, overrideUsername, overrideIconUrl, overrideIconEmoji string, props model.StringInterface, postType string, postRootId string) (*model.Post, *model.AppError) {
 	// parse links into Markdown format
 	linkWithTextRegex := regexp.MustCompile(`<([^\n<\|>]+)\|([^\n>]+)>`)
 	text = linkWithTextRegex.ReplaceAllString(text, "[${2}](${1})")
@@ -274,6 +274,9 @@ func (a *App) CreateWebhookPost(userId string, channel *model.Channel, text, ove
 		if len(overrideIconUrl) != 0 {
 			post.AddProp("override_icon_url", overrideIconUrl)
 		}
+		if len(overrideIconEmoji) != 0 {
+			post.AddProp("override_icon_emoji", overrideIconEmoji)
+		}
 	}
 
 	if len(props) > 0 {
@@ -660,7 +663,7 @@ func (a *App) HandleIncomingWebhook(hookId string, req *model.IncomingWebhookReq
 		overrideIconUrl = req.IconURL
 	}
 
-	_, err := a.CreateWebhookPost(hook.UserId, channel, text, overrideUsername, overrideIconUrl, req.Props, webhookType, "")
+	_, err := a.CreateWebhookPost(hook.UserId, channel, text, overrideUsername, overrideIconUrl, req.IconEmoji, req.Props, webhookType, "")
 	return err
 }