Fix storage class default

[npalladium]

Solves #671.

Global value overriding a specific value is confusing.

Relevant docs:

• coalesce
• default

As a sidenote, I find coalesce more natural than default unless default is used with pipelines.

Summary by CodeRabbit

• Refactor
  • Improved handling of storage class selection in volume claim templates for enhanced configuration flexibility.