[RFE] Update UI to allow enabling metrics for Backup&Restore Operator

[jbiers]

The O&B team has implemented metrics for the Backup&Restore Operator. These can currently be enabled via Helm Charts by setting these values to true:

monitoring:
  metrics:
    enabled: false

  serviceMonitor:
    enabled: false

We also want users to be able to set these via UI in cluster tools --> rancher-backup --> step 2 (the screen shown in the image):

Ideally we'd see another section below the existing "Default Storage Location" named "Monitoring". In this new section we should have the ability to turn on the metrics (Values.monitoring.metrics.enabled) and the serviceMonitor
(Values.monitoring.serviceMonitor.enabled), each independently of the other. Also, the user should only be allowed to enable the serviceMonitor via UI if rancher-monitoring is installed.

Additional context
rancher/backup-restore-operator#648