Adjusted documentation for gcs to reflect the code (#16947)

The key name for the bucket in GCS configuration is called bucket, not bucket name or bucket_name.

docs/sources/installation/configuration.md

@@ -579,7 +579,7 @@ Service Account keys can be created and downloaded from https://console.develope
 
 Service Account should have "Storage Object Writer" role. The access control model of the bucket needs to be "Set object-level and bucket-level permissions". Grafana itself will make the images public readable.
 
-### bucket name
+### bucket
 Bucket Name on Google Cloud Storage.
 
 ### path