Flesh out CanonicalMetadata

[butonic]

see https://github.com/cs3org/cs3apis/blob/master/cs3/storageprovider/v0alpha/resources.proto#L101-L104

• executable bit
• macos lables, some discussion in https://github.com/owncloud/client/issues/4511
• acls?

[labkode]

Execution bit can be added to CanonicalMetadata in: https://cs3org.github.io/cs3apis/#cs3.storage.provider.v1beta1.CanonicalMetadata

Let's start with this use-case first and tackle MacOS labels and others later.

A new field needs to be defined in the WebDAV layer so clients (desktop mainly) can understand this new capability and set local permissions accordingly:

Code    Resource    Description
S   File or Folder  is shared
R   File or Folder  can share (includes reshare)
M   File or Folder  is mounted (like on DropBox, Samba, etc.)
W   File    can write file
C   Folder  can create file in folder
K   Folder  can create folder (mkdir)
D   File or Folder  can delete file or folder
N   File or Folder  can rename file or folder
V   File or Folder  can move file or folder