feat: Add USE_GCLOUD_STORAGE_RSYNC=1 to Cloud Batch Jobs (#5017)

### Descrição:

This PR enables the `USE_GCLOUD_STORAGE_RSYNC=1` environment variable
for all containers running as part of a Cloud Batch job. This change is
intended to improve the performance and reliability of GCS operations
within these jobs by enabling `gcloud storage rsync`.

#### Context

An investigation into the Cloud Batch infrastructure revealed that the
environment variables for containers are not set via `user-data` scripts
or instance templates. Instead, they are hardcoded in the `docker run`
options string that the ClusterFuzz application builds when creating a
Batch job.

The `user-data` field in `batch.yaml` files is ignored, and the GCE
instance templates defined in Terraform are only used for persistent
bots, not for ephemeral Batch VMs.

#### Changes

This PR makes a single, targeted change to correctly inject the
environment variable:

- **Modified `src/clusterfuzz/_internal/google_cloud_utils/batch.py`**:
- The `-e USE_GCLOUD_STORAGE_RSYNC=1` flag has been added to the
`runnable.container.options` string within the `_get_task_spec`
function.

Author: hunsche

src/clusterfuzz/_internal/google_cloud_utils/batch.py

@@ -133,6 +133,7 @@ def _get_task_spec(batch_workload_spec):
       '-e HOST_UID=1337 -P --privileged --cap-add=all '
       f'-e CLUSTERFUZZ_RELEASE={clusterfuzz_release} '
       '--name=clusterfuzz -e UNTRUSTED_WORKER=False -e UWORKER=True '
+      '-e USE_GCLOUD_STORAGE_RSYNC=1 '
       '-e UWORKER_INPUT_DOWNLOAD_URL')
   runnable.container.volumes = ['/var/scratch0:/mnt/scratch0']
   task_spec = batch.TaskSpec()