Avoid counting top channel posts for posts made by plugins and OAuth apps (#20943)

* add from_integration prop to oauth posts to:
- oauth app posts
- plugin posts
- slash command responses
- incoming webhook posts

* tests

* include check for bot posts

* use from_plugin and from_oauth_app props

* fix test

* avoid counting top channel posts for posts made by plugins and oauth apps

app/plugin_api.go

@@ -630,6 +630,8 @@ func (api *PluginAPI) GetGroupsForUser(userID string) ([]*model.Group, *model.Ap
 }
 
 func (api *PluginAPI) CreatePost(post *model.Post) (*model.Post, *model.AppError) {
+	post.AddProp("from_plugin", "true")
+
 	post, appErr := api.app.CreatePostMissingChannel(api.ctx, post, true)
 	if post != nil {
 		post = post.ForPlugin()