per groupfolder storage

[icewind1991]

• Allow per-groupfolder storage #3849
• remove trashbin layout assumptions from ACL handling #3887
• Make trashbin backend storage location agnostic  #3941
• fix: make version backend storage location agnostic #3921
• refactor: remove more assumptions around groupfolder storage layout #3943
• actually setup different storages per groupfolder (this PR)

Currently groupfolders are stored under __groupfolders in the root storage, using jail mounts to mount the individual groupfolders for the users. This was done to simplify the app's code (no need for special object store handling etc) but comes with the limitation that, in multi-bucket object store setups, all groupfolder files are still stored on the same bucket.

This changes things to instead create a single storage per groupfolder (jails are still being used to separate out the files, trash and versions as separate mounts, while keeping those stored together logically).

For local primary storage, the files are now stored in $datadir/__groupfolders/$folderId/files (and $datadir/__groupfolders/$folderId/trash/$datadir/__groupfolders/$folderId/versions for trashbin/versions) where $datadir/__groupfolders/$folderId is the root of the per-groupfolder local storage.

For object store, similar logic to home storage is used to support multi-instance and multi-bucket object store but with folder ids instead of user ids.

All the new logic only affects newly created groupfolders, existing ones keep the old storage layout

[icewind1991]

/backport to stable32