Ensure a retention policy is enabled for Google Cloud Storage Buckets

Google Cloud Storage Buckets should have a retention policy with retention period greater than or equal to 90 days (7776000 seconds). It is considered best practice to set a retention period of 90 days and it is often required for framework compliance or industry regulations.

In GCP Console -

1. Log into the GCP Console and go to Cloud Storage.
2. Under Buckets, choose the bucket you wish to edit.
3. Select the Protection tab.
4. Under Retention policy, select Set Retention Policy.
5. Enter a value in the period and set the duration type, then select Save.

In Terraform -

1. In the google_storage_bucket resource, set the retention_policy.retention_period to a value in seconds.

References:
https://cloud.google.com/storage/docs/using-bucket-lock
https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/storage_bucket#nested_retention_policy