[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/post_metadata.go

@@ -55,12 +55,37 @@ func (a *App) PreparePostListForClient(originalList *model.PostList) *model.Post
 	return list
 }
 
+// OverrideIconURLIfEmoji changes the post icon override URL prop, if it has an emoji icon,
+// so that it points to the URL (relative) of the emoji - static if emoji is default, /api if custom.
+func (a *App) OverrideIconURLIfEmoji(post *model.Post) {
+	prop, ok := post.Props[model.POST_PROPS_OVERRIDE_ICON_EMOJI]
+	if !ok || prop == nil {
+		return
+	}
+	emojiName := prop.(string)
+	delete(post.Props, model.POST_PROPS_OVERRIDE_ICON_EMOJI)
+
+	if !*a.Config().ServiceSettings.EnablePostIconOverride || emojiName == "" {
+		return
+	}
+
+	if emojiUrl, err := a.GetEmojiStaticUrl(emojiName); err == nil {
+		post.AddProp(model.POST_PROPS_OVERRIDE_ICON_URL, emojiUrl)
+	} else {
+		mlog.Warn("Failed to retrieve URL for overriden profile icon (emoji)", mlog.String("emojiName", emojiName), mlog.Err(err))
+	}
+
+	return
+}
+
 func (a *App) PreparePostForClient(originalPost *model.Post, isNewPost bool, isEditPost bool) *model.Post {
 	post := originalPost.Clone()
 
 	// Proxy image links before constructing metadata so that requests go through the proxy
 	post = a.PostWithProxyAddedToImageURLs(post)
 
+	a.OverrideIconURLIfEmoji(post)
+
 	post.Metadata = &model.PostMetadata{}
 
 	// Emojis and reaction counts