[FR] dont use `:` in xattr. use `.` instead

[snoweuph]

Is your feature request related to a problem? Please describe.

I mounted a CIFS as a local disk, that supports cifsacl and xattr.
but due to it beeing cifs, it doesn't allow : inside attributes, as they can't be safely mapped to smb attributes.
thus spaces are currently brocken for me, as they use : inside xattr.

disclaimer: I know that cifs is not a supported feature, but this small change, could increase the compatibility with more filesystems and network mounted filesystems with the POSIX FS driver.

Describe the solution you'd like

don't use : in any attribute keys, instead just use another normal .
like this for example

-user.oc.grant.u:ac4f8e69-cd51-473c-ab90-cc3d2597ca0b = true
+user.oc.grant.u.ac4f8e69-cd51-473c-ab90-cc3d2597ca0b = true

Describe alternatives you've considered

a good alternative would be the option, to store the attributes in normal files, instead of xattr in a sidecar directoy like storage/metadata/xattr.
this would open up the support, for even more filesystems.
generally speaking, i think this would be alot more work, than replacing the usage of : with . for attributes.

Additional context

In cifs : is reserved for NTFS alternate data streams.
smb/cifs generally forbids the free usage of < > : " / \ | ? * in attributes.

[butonic]

related: #2073

[snoweuph]

tbh, this is what currently block me from moving to opencloud from nextcloud, as I have a storage box, which i've mounted per cifs and added as external storage in nextcloud and use as a lib for jellyfin.

with opencloud, I can only use it through an extra s3 bucket service, but then lose the file structure of the music, which breaks jellyfin features, unless I duplicated per webdav all the data, but thats just not a good solution if you have more than a few mib of music

[snoweuph]

related: #2073

kindof, though in my case I dont want opencloud to handle the remote filesystem for me.
I want to continue handeling it myself, so I can give my jellyfin access on it