Optional subtype for labels, allow grouping labels by subtype

Problem to solve

As the number of labels on a single issue increases, it becomes harder to parse. Here's an example of a gitlab-org issue with many labels:

There's a lot going on here. Colors are helpful, but it's hard to visually pick apart the number of labels here at a glance.

Proposal

Include a new optional Type field when editing a label.

When viewing an issue, group labels by their Type, if present. Here's what the first issue might look like:

Links / references