Added port-specific categories

[jimmo]

This has been requested a few times -- now that the category limit has been increased to 25 we can add a category for each port.

In the future, I hope to be able to nest the categories into groups although this feature isn't generally available yet (see https://github.com/community/community/discussions/categories/discussions for an example of what this looks like on the GitHub Community forum, which already has this feature enabled).

Also in the works from the Discussions team is the ability to subscribe just to single categories.