[BUGFIX] Fix TCA of sys_workspace custom_stages

The TCA option "appearance" is an array, with
pre-defined configuration keys. The column
"custom_stages" of the table "sys_workspace" set a
csv value for this option. This does not work.

The configuration is now transformed into the
correct array format.

Resolves: #96437
Releases: main, 11.5, 10.4
Change-Id: I25112d7ea1ce605376d70fa2dabceddd3c121faa
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72834


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>