Show how to make your own input component

In Ember Octane, we have an emphasis on teaching devs how to use Ember to interact with the DOM. We should show an example of how to create a regular `input`, as opposed to `Input`.

Showing how to write a vanilla input component serves 3 purposes:
- Teaches how to interact with the DOM
- Allows people to clearly use and understand aria properties
- empowers devs to understand the tradeoffs between input and Input, and make an informed decision
- allows people to sidestep some of the event weirdness that Input has (see https://github.com/emberjs/ember.js/issues/18654)