Add typescript

[katrynmc]

Added typescript and configured the environment to properly lint typescript files.

This PR only includes the addition of one typescript file conversion to try and focus review on the environmental changes while still having proof that the tools work as expected.

Merging this first means we can have more contributors to the conversion process.

I started going down the path of trying to make the Ember Try scenarios pass but that should probably be tackled as a separate effort. The implications for our ecosystem are non-trivial.

I'm leaving the preliminary steps here for later:
Ember Try:
Ember Try is currently failing on canary with an error (truncated): app needs ember-auto-import >= 2: ember-source
https://github.com/salsify/ember-exclaim/runs/3910286495

In order to resolve this we are going to need to do a major release:
https://github.com/ef4/ember-auto-import/blob/main/docs/upgrade-guide-2.0.md#mandatory-top-level-auto-import

This also means we need to bump Node to 12:
https://github.com/salsify/ember-exclaim/runs/3910346877

This also means adding Webpack@5 as a dev dependency.
https://github.com/salsify/ember-exclaim/runs/3910462256

[maurolemos]

All looks good to me. Thanks for bootstrapping this effort 💪

[jamescdavis]

Good call on delaying the ember-auto-import 2.x upgrade. I have ember-auto-import 2.x working in enhanced-content-ui, but we need to tread carefully with upgrading addons to ember-auto-import 2.x because:

BREAKING: addons that use ember-auto-import 2.0 require that the app also has ember-auto-import 2.0.

https://github.com/ef4/ember-auto-import/blob/main/packages/ember-auto-import/CHANGELOG.md#200

[katrynmc]

Yeah I should have been more explicit non-trivial kinda minimizes it too much 😅