Add additional types to search for when queuing up harvests

There are a few types of components that are missing from the [page where people can queue up a harvest](https://clearlydefined.io/harvest). These include:

* Maven.google artifacts
* GitLab repos
* (Soon to be deployed) Go modules

There is a massive UI/UX redesign going on right now (which will be deployed by EOY) - I'm going to hold off on adding these until that redesign is complete and deployed.