Docs - Add plugin info for `@ember/app-blueprint` apps

[TSenter]

When using the @ember/app-blueprint for apps, the Babel config is its own file instead of part of the EmberApp object. The docs should be updated to reflect this:

@ember/app-blueprint v6.8

  const {
    babelCompatSupport,
    templateCompatSupport,
  } = require('@embroider/compat/babel');

  module.exports = {
    plugins: [
      [
        'babel-plugin-ember-template-compilation',
        {
          compilerPath: 'ember-source/dist/ember-template-compiler.js',
          enableLegacyModules: [
            'ember-cli-htmlbars',
            'ember-cli-htmlbars-inline-precompile',
            'htmlbars-inline-precompile',
          ],
          transforms: [...templateCompatSupport()],
        },
      ],
      [
        'module:decorator-transforms',
        {
          runtime: {
            import: require.resolve('decorator-transforms/runtime-esm'),
          },
        },
      ],
      [
        '@babel/plugin-transform-runtime',
        {
          absoluteRuntime: __dirname,
          useESModules: true,
          regenerator: false,
        },
      ],
+     require.resolve('ember-concurrency/async-arrow-task-transform'),
      ...babelCompatSupport(),
    ],

    generatorOpts: {
      compact: false,
    },
  };

@ember/app-blueprint v6.10

  import { dirname } from 'node:path';
  import { fileURLToPath } from 'node:url';
  import {
    babelCompatSupport,
    templateCompatSupport,
  } from '@embroider/compat/babel';

  export default {
    plugins: [
      [
        'babel-plugin-ember-template-compilation',
        {
          enableLegacyModules: [
            'ember-cli-htmlbars',
            'ember-cli-htmlbars-inline-precompile',
            'htmlbars-inline-precompile',
          ],
          transforms: [...templateCompatSupport()],
        },
      ],
      [
        'module:decorator-transforms',
        {
          runtime: {
            import: import.meta.resolve('decorator-transforms/runtime-esm'),
          },
        },
      ],
      [
        '@babel/plugin-transform-runtime',
        {
          absoluteRuntime: dirname(fileURLToPath(import.meta.url)),
          useESModules: true,
          regenerator: false,
        },
      ],
+     import.meta.resolve('ember-concurrency/async-arrow-task-transform'),
      ...babelCompatSupport(),
    ],

    generatorOpts: {
      compact: false,
    },
  };

[Windvis]

It seems @ember/addon-blueprint includes 2 babel config files, and both need to contain the concurrency plugin.

I ran into the issue that concurrency tasks in published code weren't transpiled because I forgot to add the plugin to the babel.publish.config.cjs file as well.