[TASK] Add test for writing webp files via IM/GM to environment checker

This change adds test images for checking if the installed IM/GM version
can create webp images.

Similar to the pdf/ai files tests, these changes are allowed to
fail, and - if the browser does not support
webp (https://caniuse.com/webp) - will not show up either.

Resolves: #93627
Releases: master
Change-Id: Ib676f2ad096d21266aba9ee14d235377432c63c4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68166


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Daniel Sattler <sattler@b13.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Daniel Sattler <sattler@b13.de>
Reviewed-by: Benni Mack <benni@typo3.org>