[Feature]: Retrieve listing of available tags via a query

[abrenoch]

Feature description

Hi there, I'm still getting my feet wet with pimcore and the graphql functionality. I began to look into this but need to familiarize myself with the inner workings pimcore more.

I see the ability to retrieve tags as they relate to DataObjects is supported, but are there any options for retrieving a list of the tags themselves? The Pimcore\Model\Element\Tag extends the Model\AbstractModel class - is there anything that would prohibit these from being supported in a way similar to standard DataObjects?

I see the available definitions are loaded via the admin/class/get-tree route, which appears to be core functionality and probably not an option to extend, but would would it be possible tack on an extra result that points to Pimcore\Model\Element\Tag?

I'm sure there is a bit more to it than that, but does this seem like a viable option? Wanted to ask the experts before I sunk a bunch of time into this!