Provide a way to navigate to content template from the node form

Problem/Motivation

Ultimately I think this is a Canvas problem, but I'm assuming we would have to shim it for now just given the relative priority.

When you are looking at a Canvas page, the top bar Edit button takes you to the Canvas editor. When you are looking at a node, it brings you to the node edit form. This is generally fine, but if you are using Canvas content templates for the node type, it is pretty unintuitive that you have to edit a canvas page and then navigate to the content templates.

There should be a way to get to this from within the node edit form. Solution TBC, we need UX input.