Prepare for PHP 8.1

[paul-m]

This PR is part of an initiative to make sure the dependencies of DKAN are compatible with PHP 8.1.

This PR does the following, as a minor refresh to ensure testability into the near future:

• Update maximum PHPUnit version to <10, which has breaking changes.
• Update bugatino/phpcs-git-pre-commit and squizlabs/php_codesniffer to less restrictive constraints, preferring stable versions.
• Adds tooling and associated Composer scripts to facilitate local development.
• Changes for PSR-2 coding standards.
• Test classes now have setUp() method signatures to match the superclass.
• Use of #[\ReturnTypeWillChange] annotation to support jsonSerialize() methods.

[fmizzell]

Awesome... Thank you so much for all this work!

[paul-m]

🎉 thanks!

[paul-m]

It looks like the master builds are failing at the checkout step. Maybe you need to add a deploy key for circleCI?