Drop support for unsupported version of Symfony, Add Symfony 7

[tacman]

Certainly this bundle will want to add support for Symfony 7. It'd be a reasonable time to drop support for anything but ^5.4 || ^6.3 || ^7.0, and update the docs accordingly.

I can make a PR if you'd like.

5.4 will be EOL soon, too.

[vatri]

Sure, if you want make PR and I will check and merge.

Thanks for reminder!

[tacman]

Hmm. I started, but saw a few other things to change, like using attributes instead of annotations in the controller, etc. It won't be difficult, but not trivial either.