Use the Gaufrette FilesystemInterface instead of a concrete implementation

[mbabker]

Q	A
Branch?	1.11
Bug fix?	yes
New feature?	yes
BC breaks?	no
Deprecations?	no
Related tickets	N/A
License	MIT

The image uploader has a dependency to a concrete class instead of the interface. This widens the parameter type to allow the interface.

[GSadee]

The base of this pull-request was changed, you need fetch and reset your local branch
if you want to add new commits to this pull request. Reset before you pull, else commits
may become messed-up.

Unless you added new commits (to this branch) locally that you did not push yet,
execute git fetch origin && git reset "patch-1" to update your local branch.

Feel free to ask for assistance when you get stuck 👍

[GSadee]

Thanks, Michael! 🥇