Use co-location in the addon package

[BlueCutOfficial]

This PR is a step to convert the addon to v2. Now that we have a monorepo structure, we can work on meeting all the prerequisites before doing the actual conversion.

The present change is about using co-located templates.

Details:

The porting-addons-to-v2.md states the following:

Make sure your addon has co-located templates. By default, the build tools expect to find the component's .js and .hbs in the same folder. If your addon used to have an addon/templates/components folder, move to co-location. Note that a codemod has been released when co-location has become the recommended structure.

If we don't use co-location, the .js and the .hbs are compiled as two different components, the latter being template-only.