[TASK] Add cancel button to dashboard add widget modal

The add widget modal has a cancel button on the bottom
of the modal now to match the other modal windows in
the backend.

Resolves: #103787
Releases: main, 12.4
Change-Id: I0c2c970b1148dfddadff1c3722d04dfcc939a69d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84142


Reviewed-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Jörg Bösche <typo3@joergboesche.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>