Introduce new API fields to enable resource protection

This MR adds new API fields to SylvaUnitsRelease to prevent accidental deletion of management cluster resources.

New fields:

• spec.metadata.labels/spec.metadata.annotations - Apply custom metadata to all managed resources
• spec.prune (default: true) - When false, deleting the SylvaUnitsRelease removes owner references from managed resources instead of deleting them

Implementation:

• Renamed Metadata  to ManagedResourceMetadata to avoid ambiguity.
• Removed duplicate struct from common ; refactored cleanManagedResources to take an explicit disownOnly parameter
• Added integration test for prune=false behaviour

covers #53 (closed)

MR raised in sylva-core sylva-projects/sylva-core!6650 (closed)