Merge pull request #27981 from a-robinson/journal-cvm

Automatic merge from submit-queue

Support journal logs in fluentd-gcp on GCI

This maintains a single common image for each rather than having to fork out separate images, relying on different commands in yaml manifests to differentiate in the behavior. This is treading on top of @adityakali's #27906, but I wasn't able to get in touch with him this afternoon until very recently. He's handling making sure that the new yaml manifests are used when running on GCI.

```release-note
```

cluster/saltbase/salt/fluentd-gcp/fluentd-gcp.yaml

@@ -1,3 +1,5 @@
+# This config should be kept as similar as possible to the one at
+# cluster/addons/gci/fluentd-gcp.yaml
 apiVersion: v1
 kind: Pod
 metadata:
@@ -9,7 +11,7 @@ spec:
   dnsPolicy: Default
   containers:
   - name: fluentd-cloud-logging
-    image: gcr.io/google_containers/fluentd-gcp:1.20
+    image: gcr.io/google_containers/fluentd-gcp:1.21
     resources:
       limits:
         memory: 200Mi