Update Coder plugin to work in isolated dev mode

One of the big points that Backstages stresses in their docs is that plugins should be able to be spun up in isolation. You shouldn't need to bring in a whole Backstage deployment to test component changes.

The Coder plugin is a frontend plugin that relies on a proxied endpoint to the main Coder API. It can be spun up in isolation, but because it's missing a backend proxy, the component will never populate with data.

[As mentioned here](https://github.com/coder/backstage-plugins/pull/2#pullrequestreview-1883966805), API factories might do the trick, but they're not as well-documented, and they still require testing. Depending on how much needs to change, we might need to revamp our plugin's API calls, too.

Commencez par les appels d'API du Coder frontend plugin et comparez son isolated-dev setup avec le backend proxy manquant. Évaluez l'approche API-factory référencée dans pull request #2 et testez le plugin de manière isolée ; cela signifie que le composant se remplit de données sans déploiement complet de Backstage.

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