Allow Symfony 6 installation & support

[santakadev]

There is no code change in the library. This PR:

• Allow the installation through composer in Symfony 6 applications
• Update the installation documentation

Unit tests continue working. I've also tested it manually in a Symfony 6.2 app, and it works as expected.

[SebTM]

Hey, I wanted to ask if we could craft a release from it to be able to install it regularly by tag instead of dev-master when using Symfony 6.X?