Investigate switching from ember-cli-addon-docs to field-guide

[elwayman02]

https://github.com/empress/field-guide

ec-addon-docs is in maintenance mode and is mostly a dead project. We should investigate rebuilding the demo and documentation in field-guide instead.

[elwayman02]

This may help address #482 as well.

[mrloop]

ember-cli-addon-docs is also preventing the addon from building. ember-auto-import 2.x needs webpack 5.x as a devDependency, adding it and the build fails until ember-cli-addon-docs* are removed, then the build works. See https://github.com/mrloop/ember-user-activity/tree/em-build for build which passes yarn ember t

An alternative approach I've seen is updating the addon to a v2 monorepo so the dummy/test app is a seperate pkg and dependencies get be changed independently.