[BUGFIX] Make submit button save all tabs in extension manager

Each category is rendered as separate sheets/tabs, but should
share a single form and submit button. Otherwise changes to
one sheet are not saved when clikting submit in another sheet.

Fixes: #44876
Related: #44559
Releases: 6.1, 6.0

Change-Id: Idce5c70c20faebe495b9241ac0f2f0ea0aec6c2a
Reviewed-on: https://review.typo3.org/17760
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn