Make app-template-minimal more minimal

[NullVoxPopuli]

Make the minimal template super minimal.

Learnings along the way:

• we get to use type=module
• we get to use package.json#imports
• we can use src instead of app
• we don't need a config directory
• we still have to have ember-cli (for running tests)
• ember-cli does not auto-detect a testem.cjs file, so we must use
  --config-file

Things that need to happen, but haven't yet, because I think we should make a better API in macros for this:

import { getGlobalConfig } from '@embroider/macros/src/addon/runtime';

const ENV = {
  modulePrefix: 'limber',
  environment: import.meta.env.DEV ? 'development' : 'production',
  rootURL: '/',
  locationType: 'history',
  EmberENV: {},
  APP: {},
};

export default ENV;

export function enterTestMode() {
  ENV.locationType = 'none';
  ENV.APP.rootElement = '#ember-testing';
  ENV.APP.autoboot = false;
  getGlobalConfig()['@embroider/macros'].isTesting = true;
}

otherwise macroCondition(isTesting()) always hits the else branch