Add ddev

This is super cool and helpful to start up a development environment for Recurring Events, thanks for starting this!

I am trying out the features. So far I had an error when running ddev phpstan but this is already fixed in the new release of the project.

For the moment ddev phpunit doesn't work. I'm getting PHP Fatal error: Uncaught Error: Class "Drupal\Tests\BrowserTestBase" not found in /var/www/html/tests/src/Functional/LoadTest.php:15.

I got PHPUnit to work by simple removing our custom phpunit.xml file which was not making DDEV happy.

Some PHPStan failures have popped up now, but these are not caused by this issue, but by some recent changes in the 3.0.x branch. Ref. 🐛 PHPStan failures in 3.0.x branch Active .

Thanks very much for the contribution! This will make it easier for the community to contribute to the module :)