Rename the CRD's finalizer name

[terassyi]

What

Rename finalizer from coil.cybozu.com to coil.cybozu.com/finalizer.

New coil's CRD can add finalizers that don't have /.
In the future, CRD's finalizers also will need to have /.

ref: kubernetes/kubernetes#119508

How

Coil adds the finalizer like following.

coil/v2/api/v2/addresspool_webhook.go

Line 28 in 5653f1d

func (r *AddressPool) Default() {

We have to rename its name and migrate existing finalizers.

Checklist

• Finish implentation of the issue
• Test all functions
• Have enough logs to trace activities
• Notify developers of necessary actions