[scheduler] Layer os became mandatory

[sericicole]

Describe the bug
Since frame dispatching was offload from cuebot, submiting a job with os.environ['OL_OS']='your_os' or outline.cuerun.launch(job, use_pycuerun=False, os='your_os') is mandatory.

This is due to the validate_match function.

fn validate_match(
    host: &Host,
    _layer_id: &Uuid,
    show_id: &Uuid,
    cores_requested: CoreSize,
    allocation_service: &AllocationService,
    os: Option<&str>,
) -> bool {
    // Check OS compatibility
    if host.str_os.as_deref() != os {
        return false;
    }

To Reproduce
Submit a job without OL_OS or no os option with outline
No job will be dispatched. Wasn't able to find suitable hosts for group and NoCandidateAvailable will appear, when the loggin level is set to debug.

Expected behavior
If no layer os is provided, all host should satisfy the condition.

Maybe updating the function with if os.is_some() && host.str_os.as_deref() != os can be an option.

Version Number
1.15