helm/SV : make PVC volume name overridable to have several SV on same cluster without having to use separate namespaces

Same issue as #337 but for SV

```
./splice-sv-node/templates/sv.yaml:369:            claimName: "sv-app-global-domain-migration-pvc"
./splice-sv-node/templates/sv.yaml:407:  name: "sv-app-global-domain-migration-pvc
```

