[cetic/nifi] support extraVolumeClaimTemplates

[chicco785]

We have the need to install also a volume for extensions. The issue is that we don't have a
shared filesystem to mount, so each instance needs it's pvc, which his hard to configure via extraVolume

Is your feature request related to a problem? Please describe.

We need to mount a volume for extensions.

Describe the solution you'd like

a parameter extraVolumeClaimTemplates that we could use to pass custom volume claim templates.

Describe alternatives you've considered

shared file system

Additional context
Add any other context or screenshots about the feature request here.