Migrate to adopted-ember-addons

## Addon Transfer Checklist from the [guidelines](https://github.com/adopted-ember-addons/program-guidelines/blob/master/README.md)

- [x] Update the package.json repository field to point to the new location
- [x] If any demo URL or homepage is referenced, it should be updated. At the very least, file an issue on the repo so the adopter can fix See https://github.com/thefrontside/emberx-select/issues/241
- [x] Ensure Release practices are documented
- [x] Add `MelSumner` to the maintainers of the package on `npm`. Remove other maintainers.

The issue lists an addon transfer checklist: package.json repository field, demo or homepage URLs, release practice documentation, and npm maintainers. All items are already checked, and one related item points to issue #241, so first verify whether any migration work remains. Done would mean a maintainer confirms an unchecked remaining transfer task, not just reopening old completed checklist items.

Rédigé par le modèle d'indexation à partir du texte de l'issue.