Support xattrs in syncthing

[nwmcsween]

Describe the feature you'd like to have.

Syncthing with sendXattr/syncXattr by default

What is the value to the end user? (why is it a priority?)

Needed for various applications that use xattrs for additional data such as samba

How will we know we have a good solution? (acceptance criteria)

samba sysvol replication works correctly

Additional context

[tesshuflower]

@nwmcsween A few things might get in the way of us trying to do this:

• we've had issues in the past with syncing xattrs, with restic this could cause issues in selinux envs where we don't have full root permissions. In the end we needed to update restic to have it only sync user level xattrs. I don't believe xattr syncing worked at all without running in privileged mode, so I'd imagine even if we supported this you might need to annotate your namespace to tell the mover to run privileged: Support xattrs in syncthing #1715

• Additionally, xattr support is just one of many syncthing options - I'm not sure the best way to allow this specific update - potentially we could expose something in a config map or something of the sort to allow you to override the entire restic config - this makes it pretty easy to break things however.