async generateGCSBucket() {
    const name = BucketManager.generateBucketName();
    const bucket = this.storage.bucket(name);
    this.gcsBuckets.push(bucket);

    await bucket.create();
    await this.grantSTSPermissions(bucket);

    return bucket;
  }
Generates a unique GCS bucket for testing.
Configures STS read/write perms on the bucket.

Is cached for easy clean-up via {#deleteBuckets}.