Fix #1652, #1647: Fix v3 migration diffs for metadata, postrender, set_list defaults, and version normalization

[dennismdejong]

Changes

Fixes unexpected diffs encountered during v3 plugin framework migration:

helm/resource_helm_release.go

• Fix v-prefix version diff: Use .ValueString() instead of .String() in ModifyPlan version comparison so TrimPrefix("v") correctly compares versions regardless of leading 'v'.
• Fix metadata recompute: Use versionsEqual() for version comparison in recomputeMetadata to handle v-prefix differences.
• Fix set ordering diffs: Compare set, set_sensitive, and set_list entries order-independently by sorting before comparison, preventing false diffs when the server returns entries in different order.

helm/resource_helm_release_stateupgrader.go

• Fix postrender null diff: Preserve old null/empty postrender as null instead of creating an empty object with default values.
• Fix set_wo_revision default: Change default from 1 to 0 when write-only sets are not used.

Related Issues

• Closes updating to v3 results in unexpected diff in plans #1652
• Closes Helm Provider Upgrade to 3.0.1 Introduces Unexpected Behavior with postrender, Namespace Resolution and Version Drift #1647