Use unique names for logging buckets in examples

Logging bucket name can be reused only after 7 days (when it is actually
deleted). When different tests reuse the same name, the ones that are
executed as 2nd and later will fail with message:
```
Error updating Logging Bucket Config [...]: googleapi: Error 400: Buckets
must be in an ACTIVE state to be modified
```

As their actual state is:
```
lifecycleState: DELETE_REQUESTED
```

modules/organization/README.md

@@ -291,7 +291,7 @@ module "bucket" {
   source      = "./fabric/modules/logging-bucket"
   parent_type = "project"
   parent      = var.project_id
-  id          = "bucket"
+  id          = "${var.prefix}-bucket"
 }
 
 module "org" {