add'l codegen for docs/fields.md

this one feels the most potentially problematic, so just split it into its own commit
- though it's still generated, so still impacted by the other commits of this PR

Signed-off-by: Anton Gilgur <agilgur5@gmail.com>

docs/fields.md

@@ -5123,6 +5123,24 @@ ObjectReference contains enough information to let you inspect or modify the ref
 |`resourceVersion`|`string`|Specific resourceVersion to which this reference is made, if any. More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#concurrency-control-and-consistency|
 |`uid`|`string`|UID of the referent. More info: https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#uids|
 
+## Duration
+
+Duration is a wrapper around time.Duration which supports correctmarshaling to YAML and JSON. In particular, it marshals into strings, whichcan be used as map keys in json.
+
+<details>
+<summary>Examples with this field (click to open)</summary>
+<br>
+
+- [`pod-gc-strategy-with-label-selector.yaml`](https://github.com/argoproj/argo-workflows/blob/master/examples/pod-gc-strategy-with-label-selector.yaml)
+
+- [`pod-gc-strategy.yaml`](https://github.com/argoproj/argo-workflows/blob/master/examples/pod-gc-strategy.yaml)
+</details>
+
+### Fields
+| Field Name | Field Type | Description   |
+|:----------:|:----------:|---------------|
+|`duration`|`string`|_No description available_|
+
 ## LabelSelector
 
 A label selector is a label query over a set of resources. The result of matchLabels and matchExpressions are ANDed. An empty label selector matches all objects. A null label selector matches no objects.