fix: revert the removal of the default importMap location

[auratiger]

Description

Fixes: #7803

• I have read and understand the CONTRIBUTING.md document in this repository.

Type of change

• Chore (non-breaking change which does not add functionality)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Change to the templates directory (does not affect core functionality)
• Change to the examples directory (does not affect core functionality)
• This change requires a documentation update

Checklist:

• I have added tests that prove my fix is effective or that my feature works
• Existing test suite passes locally with my changes
• I have made corresponding changes to the documentation

What?

This is a revert of the removal of the default importMap location here: 8085

Why?

When configuring a custom admin route, such as:

  routes: {
    admin: '/admin/490d6a65bf0f8309e5915779',
  },

you are not able to use dynamic routes like app/(payload)/admin/[slug]/ and without a default path location
you are forced to hard code the route for the generate:importmap command to work.
I believe leaving the default path, gives people more freedom of customizing the admin routes.