Drop compatibility with unsupported versions of Symfony and PHP

[tacman]

Currently the bundle allows for very old and unsupported versions of Symfony. Is there any benefit to dropping that, especially since we'll be adding Symfony 6 support (#3)

    "symfony/finder": "^3.4 || ^4.0 || ^5.0",
    "symfony/framework-bundle": "^3.4.24 || ^4.0 || ^5.0",

Maybe there's no benefit to dropping support for before 4.4, but I'd hate to see improvements being held back because of support for unsupported versions.

Ditto on support for 7.3, so the bundle can use some features from 7.4.

Thoughts?

[bertrandseurot]

Note : nelmio/alice already requires php 7.4

[theofidry]

Fixed with the new release