Feature/update php jwt use php8

[gabrielberthier]

Open support for PHP versions above 8.0 and include php-jwt ^6.0.
Some refactors were made in order to use some features in the future as named parameters, typed properties and so on.
Since using multiple keys are not usual, I personally preferred to remove support for this feature, as it usually leads to difficulty in regard of maintaining keys secure and less prone to misleading behaviour.

[gabrielberthier]

Updated codebase in order to still use multiple keys.

[esetnik]

@tuupola are you looking for maintainers? Seems like this PR solves a bunch of the compatibility issues.

[tuupola]

Actually I am pondering giving away maintainership of some of the PHP projects including tuupola/slim-jwt-auth and tuupola/slim-basic-auth. Currently paid work comes first and paid work is mostly Kubernetes and stuff.

[esetnik]

Hi @tuupola I would be interested in joining as a maintainer on this project to help move it forward. Please let me know if that's something you'd like.

[gabrielberthier]

In case I can help with something else, let me know. Also, if there is more to implement at this PR, I'd be glad to do it as well.

[zwalden]

@tuupola any reason this hasn't been moved forward?

Is there any help needed here to push this forward?

Happy to lend some assistance if helpful.

[zluiten]

Such a shame to see this project die :'(