[BUGFIX] Migrate `legend` configuration of chart widgets

Due to the major update of the `chart.js`
package to v4, corresponding `legend`
configuration of the BarChartWidget
and the DoughnutChartWidget needs to
be migrated.

Resolves: #102759
Releases: main, 12.4
Change-Id: Iced423d184a86b334390cad21319bf088a8369a1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82385


Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>