Apply default values in Terraform and CloudRun Deployment plugin

[rawadhossain]

What this PR does:
Implements setting default values in the CloudRun and Terraform deployment plugins by adding UnmarshalJSON methods that call defaults.Set().

Why we need it:

• CloudRun’s ServiceManifestFile was documented to default to service.yaml, but the default was never applied.
• Terraform’s DriftDetectionEnabled had a default true tag but the value was never set during unmarshaling.

Part of Issue #6174

Does this PR introduce a user-facing change?:

• How are users affected by this change:
  • CloudRun configs that omit serviceManifestFile will now correctly default to service.yaml
  • Terraform deploy target configs that omit driftDetectionEnabled will now correctly default to true
• Is this breaking change: No
• How to migrate (if breaking change): N/A