Create an issue template

There are several categories of issues that are being posted.
A bunch of them are not galaxy_codex issues but [usegalaxy-au/galaxy-labs-engine](https://github.com/usegalaxy-au/galaxy-labs-engine) issues. I propose an issue template like:

> **Do you have a Labs Issue?**
> - If your issue relates to features of the Labs Engine, please post an issue [here](https://github.com/usegalaxy-au/galaxy-labs-engine/issues) instead. Example: "Can I do X in a Galaxy Lab?", "The Labs documentation does not mention X", "I got this error on my Lab page".
> - If your issue relates to the content of a Lab, please proceed to post an issue here. Example: "Genome Lab Assembly tools are outdated"