By default, Payload only attempts to locate the import map file in the following locations:
- `src/app/(payload)/{adminroute}/importMap.js`
- `app/(payload)/{adminroute}/importMap.js`
This is fine for most projects, but sometimes you may want to place the import map - or the Payload admin directory - somewhere else.
This PR adds a new `importMapFile` property that allows you to override this heuristic and specify your own import map path.