Optimize FileSystemTags workflow for groupfolder

In https://github.com/nextcloud/server/pull/28774

 we disabled the
caching for the groupfolder application since it worked due to the fact
that in groupfolders, getFileIds could be called with the same $cacheId
and path for actually different groupfolders.

This revert this change and instead add the folderId from the
groupFolder to the cacheId. This solve the issue of the uniqueness of
the cacheId inside GroupFolder. Downside is that we introduce
groupfolder specific implementation inside the server repo.

The seconf optimization is to not consider paths starting with
__groupfolders in executeCheck. This is due to the fact that files in
the groupfolder application call two times executeCheck one time with
the url __groupfolder/<folderId>/<path> and the other time with <path>.
The first time will always return an empty systemTags array while the
second call will return the correct system tags.

Signed-off-by: Carl Schwan <carl@carlschwan.eu>