Add option to disable rsync xattrs/acls in build process

[fmo008]

Describe the solution you'd like:
Currently, elemental hardcodes --xattrs and --acls in the rsync command during ISO building. This can cause failures when building on systems where security.selinux attributes cannot be modified (e.g., containers, non-SELinux hosts, or CI environments).

The error typically appears as:
lremovexattr failed: Permission denied

This forces users to patch the source code manually.

Proposed Solution

Add a configuration option to disable these flags:

rsync:
  enableXattrs: false
  enableAcls: false

**Environment:**

- Elemental release version (use `cat /etc/os-release`): v1.1.7+

[frelon]

Hi @fmo008

That's a nice idea! If you have some time we would really appreciate a PR!