Composer: Add seld/jsonlint as dependency

[nhaagen]

This PR adds seld/jsonlint as composer dependency.

Usage:

• This allows the setup to give more informative error messages regarding the json that is used for config.

Wrapped By:

• Not applicable, functionality is only used internally in the setup and not provided to other ILIAS components.

Reasoning:

• The PHP json parser does not give information where a given json is faulty. This degrades user experience since we can only say "your json is wrong" but not where the actual error is located.

Maintenance:

• The library received its last update in July '24. It seems to be feature complete, though.
• The maintainer Jordi Boggiano works on packagist and composer and is a well known person in the PHP community.
• The functionality provided by this library is not super important but more for quality of life. We could easily decide to ditch the library if any problems arise.

Links:

• Packagist: https://packagist.org/packages/seld/jsonlint
• GitHub: https://github.com/Seldaek/jsonlint

[klees]

License is GPLv3.

[klees]

License is MIT.

[kergomard]

Dependency is accepted for ILIAS 11. Licence: MIT.