[BUGFIX] Ignore permission checks for processed files

It must be possible that processed files are generated
even if the user has read only permissions on a storage.

Additionally add a method to Storage, to specifically
update a processed file with a local file.

Resolves: #51209
Releases: 6.0, 6.1, 6.2

Change-Id: I847b02f070c55647e06695c1c70b0b7e8e238177
Reviewed-on: https://review.typo3.org/23196
Reviewed-by: Frans Saris
Tested-by: Frans Saris
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind