Decouple frontend rebuilds from API changes while developing locally

[apburnes]

To improve rebuild times while developing locally, decouple the automatic, complete rebuild of the frontend application whenever the API is updated. Currently, a full rebuild of the frontend when a change occurs in the API but we do an incremental rebuild of the frontend when changes occur to it. Switching to use only incremental frontend builds after initial start will mean no long delays between changes.

Notes

• The [devMiddleware function](https://github.com/cloud-gov/pages-core/blob/main/api/middlewares/dev-middleware.js) that currently rebuilds the entire frontend

Acceptance Criteria

• Decouples the frontend build triggered by changes to the api
• Removes the devMiddleware function
• Only run incremental frontend builds after initial start up