add imagick PHP extension back for PHP 8.x

[dossy]

Description

PHP 8.x Docker images are missing the imagick PHP extension. This PR brings them back.

Bonus: This PR also adds WebP support to PHP 7.4 and PHP 8.x's GD extension.

Fixed Issues (if relevant)

1. magento/magento-cloud-docker#357: Incompatibility with Magento >= 2.4.0 (Imagick missing)

Fixes #357.

Manual testing scenarios

1. php bin/ece-docker image:generate:php
2. Add the context images to your docker-compose.override.yml's services like this:

services:
  fpm:
    build:
      context: ./vendor/magento/magento-cloud-docker/images/php/8.1-fpm
      dockerfile: Dockerfile
  fpm_xdebug:
    build:
      context: ./vendor/magento/magento-cloud-docker/images/php/8.1-fpm
      dockerfile: Dockerfile
  generic:
    build:
      context: ./vendor/magento/magento-cloud-docker/images/php/8.1-cli
      dockerfile: Dockerfile
  build:
    build:
      context: ./vendor/magento/magento-cloud-docker/images/php/8.1-cli
      dockerfile: Dockerfile
  deploy:
    build:
      context: ./vendor/magento/magento-cloud-docker/images/php/8.1-cli
      dockerfile: Dockerfile

3. docker compose build fpm
4. docker compose run --rm fpm php -i | awk '/imagick module/,/^$/'
5. Look for imagick module => enabled in the output from step 4.
6. docker compose run --rm fpm php -i | awk '/GD Support/,/^$/'
7. Look for WebP Support => enabled in the output from step 6.

Release notes

• Add imagick PHP extension back to PHP 8.x Docker images.
• Add WebP support to PHP 7.4 and PHP 8.x's GD extension in Docker images.

Associated documentation updates

Add link to Magento DevDocs PR or Issue, if needed.

Contribution checklist

• Pull request has a meaningful description of its purpose
• Pull request introduces user-facing changes and includes meaningful release notes and documentation
• All commits are accompanied by meaningful commit messages

[dossy]

Closing and re-opening after signing CLA.