fix(helm): omit unset rbd mirror daemon count

[tomatotomata]

Summary

When a cephConnections entry omits rbdMirrorDaemonCount, the chart currently renders rbdMirrorDaemonCount: null. Kubernetes rejects that value because the CRD field is an optional integer with a minimum of 1.

Render the field only when a value is supplied. Existing positive values are unchanged, while omitted values now let the CRD/operator default apply.

Testing

• Rendered the chart with an unset value and confirmed the field is omitted.
• Rendered the chart with rbdMirrorDaemonCount=2 and confirmed the field remains 2.
• git diff --check

Fixes #551