Simplify Drupal Drush configuration

[pjcdawkins]

Why

Parallel to platformsh-templates/drupal11#11

Simplify Drush configuration removing the need for a ./drush/upsun_generate_drush_yml.php file.

What's changed

• Move now-unnecessarily complex Drush configuration from a PHP script to a couple of lines in .environment
• Remove now unnecessary reference to the config-reader library for Upsun + Drupal
• Remove dependencies which was unnecessarily requiring Composer 2 (it's default in PHP 8.2+)
• Inline the deploy script

I'm ignoring the nextjs-drupal template and tutorial (we could handle that separately?), and ancient Drupal versions (< 10).

Where are changes

Updates are for:

• platform (sites/platform templates)
• upsun (sites/upsun templates)

[github-actions]

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See the changed pages:

Platform.sh docs

• https://simplify-drupal-11-gqlcqxy-ucq44jg6ofare.eu-5.platformsh.site/guides/drupal/deploy/customize.html

Upsun docs

• https://docs.upsun.com.simplify-drupal-11-gqlcqxy-ucq44jg6ofare.eu-5.platformsh.site/get-started/stacks/drupal.html