garbage collection: add blurb about ImageMaximumGCAge

Signed-off-by: Peter Hunt <pehunt@redhat.com>

content/en/docs/concepts/architecture/garbage-collection.md

@@ -137,6 +137,20 @@ collection, which deletes images in order based on the last time they were used,
 starting with the oldest first. The kubelet deletes images
 until disk usage reaches the `LowThresholdPercent` value.
 
+#### Garbage collection for unused container images {#image-maximum-age-gc}
+
+{{< feature-state for_k8s_version="v1.29" state="alpha" >}}
+
+As an alpha feature, you can specify the maximum time a local image can be unused for,
+regardless of disk usage. This is a kubelet setting that you configure for each node.
+
+To configure the setting, enable the `ImageMaximumGCAge`
+[feature gate](/docs/reference/command-line-tools-reference/feature-gates/) for the kubelet,
+and also set a value for the `ImageMaximumGCAge` field in the kubelet configuration file.
+
+The value is specified as a Kubernetes _duration_; for example, you can set the configuration
+field to `3d12h`, which means 3 days and 12 hours.
+
 ### Container garbage collection {#container-image-garbage-collection}
 
 The kubelet garbage collects unused containers based on the following variables,
@@ -178,4 +192,4 @@ configure garbage collection:
 
 * Learn more about [ownership of Kubernetes objects](/docs/concepts/overview/working-with-objects/owners-dependents/).
 * Learn more about Kubernetes [finalizers](/docs/concepts/overview/working-with-objects/finalizers/).
-* Learn about the [TTL controller](/docs/concepts/workloads/controllers/ttlafterfinished/) that cleans up finished Jobs.
+* Learn about the [TTL controller](/docs/concepts/workloads/controllers/ttlafterfinished/) that cleans up finished Jobs.