[FEATURE] Add a timestamp when downloading an extension

When downloading an extension within the Extension Manager, a
timestamp should be automatically added to the filename.

Resolves: #50441
Releases: 6.2
Change-Id: I86c00b814715b126a655f2c73b40b955b328acff
Reviewed-on: https://review.typo3.org/22669
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe