Add a ddev command and shell helper for Drupal core's dr CLI

[amateescu]

• Adds a commands/web/dr DDEV command that runs core's new dr CLI (shipped since 11.4 as core/scripts/dr, exposed at vendor/bin/dr), with a friendly error on older core checkouts.
• Adds a dr shell helper so the bare command auto-delegates to DDEV, and updates the helper lists in the README, cheat sheet and post-install message.
• Documents usage in the README and DRUPAL-DEV.md.
• Extends health_checks in the bats tests with ddev dr list.

[rfay]

Hmm, DDEV v1.25.3 already has ddev dr - Why have this?

[amateescu]

@rfay because I don't read release notes 🤦 Opened a new PR to remove the command, but keep its shell helper :) #29