mgr: setting balancer mode from cluster spec.

[sp98]

This PR adds a settings option in the Module struct which can help users to futher customize the balancer module with a differet mode.

Testing: updated the balancer mode to crush-compat.

kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.
sh-4.4$ ceph balancer status 
{
    "active": true,
    "last_optimize_duration": "0:00:00.000653",
    "last_optimize_started": "Fri May 17 07:59:01 2024",
    "mode": "crush-compat",
    "no_optimization_needed": false,
    "optimize_result": "Distribution is already perfect",
    "plans": []
}
sh-4.4$ exit

Checklist:

• [ ] Commit Message Formatting: Commit titles and messages follow guidelines in the developer guide.
• [ ] Reviewed the developer guide on Submitting a Pull Request
• [ ] Pending release notes updated with breaking and/or notable changes for the next minor release.
• [ ] Documentation has been updated, if necessary.
• [ ] Unit tests have been added, if necessary.
• [ ] Integration tests have been added, if necessary.