Add example to the CRD for what the size should be for Servicability spec

[danielguinan1]

This is a very basic change, but as someone with little experience in storage types when I tried just 1 either the operator or ceph did not like that. May be helpful to have an example showing the user that a storage type is also needed in it.

This is what currently is given when making the OLA from the UI:

A convenient field to request the size of the persisted storage to use for serviceability.

Could be helpful if it had something like:

A convenient field to request the size of the persisted storage to use for serviceability. (ex: 1Gi)