[FEATURE] Integrate possibility to extend workspace module

The workspace module only can be extended by overriding PHP and
JavaScript components. This feature aims to integrate a possibility
to extend the definition and behaviour of displayed columns in the
workspace module.

Change-Id: I8ba18c8e35bfc09a5a34becaa66b6543ad73ee01
Resolves: #50219
Releases: 6.2
Reviewed-on: https://review.typo3.org/22444
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader