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

[github-actions]

This PR is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 7 days.

[rawadhossain]

Hi @Warashi, just checking in since it was marked stale and may auto close soon.
Would appreciate your review or any feedback when you have time. I'm happy to make changes if needed. Thanks.

[Warashi]

LGTM