[MM-38239 & MM-39788] Recent files causing crash (#18942)

* wip

* adding tests for new endpoint

* tool updates

* new function for getting postsByIds

* fixing test

* adding limit of 1000 to post query

* fixing PR comments

* fixing permission logic

Co-authored-by: Collin <collineng@gmail.com>
Co-authored-by: Collin Eng <eng.engineereng@gmail.com>
Co-authored-by: Benjamin Cooke <benjamincooke@Benjamins-MacBook-Pro.local>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Benjamin Cooke <benjamincooke@Benjamins-MBP.ht.home>

app/post.go

@@ -1670,3 +1670,18 @@ func (a *App) GetPostIfAuthorized(postID string, session *model.Session) (*model
 
 	return post, nil
 }
+
+func (a *App) GetPostsByIds(postIDs []string) ([]*model.Post, *model.AppError) {
+	posts, err := a.Srv().Store.Post().GetPostsByIds(postIDs)
+	if err != nil {
+		var nfErr *store.ErrNotFound
+		switch {
+		case errors.As(err, &nfErr):
+			return nil, model.NewAppError("GetPostsByIds", "app.post.get.app_error", nil, nfErr.Error(), http.StatusNotFound)
+		default:
+			return nil, model.NewAppError("GetPostsByIds", "app.post.get.app_error", nil, err.Error(), http.StatusInternalServerError)
+		}
+	}
+
+	return posts, nil
+}