Composer: add filp/whoops as dependency

[nhaagen]

This PR adds filp/whoops as composer dependency.

Usage:

• Used for formatting error messages for consumation by developers via browser and for error reports.

Wrapped By:

• Not applicable. This is used in error handling code that does not provide interfaces to other ILIAS code.

Reasoning:

• filp/whoops is a mature and stable library that produces comprehensible output of errors, exceptions and the environment they have been created in. Good error reporting boosts productivity of developers and admins alike.

Maintenance:

• The library and its are stable for a long time now. Major version hasn't been bumped for > 7 years now.
• Patch version is bumped regularly to deliver fixes. Last version has been published September '24. Hence maintenance seems to be stable.
• There is a corporate sponsor of this library.

Links:

• Packagist: https://packagist.org/packages/filp/whoops
• GitHub: https://github.com/filp/whoops

[klees]

License is MIT.

[kergomard]

Dependency is accepted for ILIAS 11. Licence: MIT.