Docs: Add list of supported k8s versions for agent injector (#16433)

website/content/docs/platform/k8s/injector/index.mdx

@@ -20,6 +20,21 @@ the request. This functionality is provided by the [vault-k8s](https://github.co
 project and can be automatically installed and configured using the
 [Vault Helm](https://github.com/hashicorp/vault-helm) chart.
 
+## Supported Kubernetes Versions
+
+The following [Kubernetes minor releases][k8s-releases] are currently supported.
+The latest version of the injector is tested against each version. It may work
+with other versions of Kubernetes, but those are not supported.
+
+* 1.24
+* 1.23
+* 1.22
+* 1.21
+* 1.20
+* 1.19
+
+[k8s-releases]: https://kubernetes.io/releases/
+
 ## Overview
 
 The Vault Agent Injector works by intercepting pod `CREATE` and `UPDATE`