Add a config for <https://www.gitpod.io/>. This allows users to easily run an online IDE pre-configured to develop and test Gitea by opening <https://gitpod.io/#https://github.com/go-gitea/gitea>. [![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/go-gitea/gitea) Co-authored-by: 6543 <6543@obermui.de> Co-authored-by: techknowlogick <techknowlogick@gitea.io>