### Motivation
In some case, my k8s node only have 1 large capacity ssd, for deploying 1 bookie, I need:
- Partition the ssd into 2 disks, and make 2 pv over it.
- Just make 1 pv over it, but journal & ledgers under same mount path (this PR did)
Both can't isolate IO for journal & ledgers, so I prefer the second one for reusability.
### Modifications
values.yaml
- add `useSingleCommonVolume` option, default false
bookkeeper-statefulset.yaml
- mount the only PV to path `/pulsar/data/bookkeeper`
- use configured common storageClassName
bookkeeper-storageclass.yaml
- use configured provisioner for the common storageClass
### Others
This may not be an issue for everyone, if it's not necessary to merge, I'll just use it locally
### Verifying this change
- [x] Make sure that the change passes the CI checks.
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