[TAKS] Add json as composer dependency

PHP extension json is now listed as dependency
 in composer.json. Extension mysqli is added to
 "suggest" section.

Resolves: #74005
Releases: master, 7.6
Change-Id: Iae0f388a4b10a24e98c392f878381d753971acdb
Reviewed-on: https://review.typo3.org/47006


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>