Add StrictIPCIDRValidation feature gate file

Author: danwinship

content/en/docs/reference/command-line-tools-reference/feature-gates/StrictIPCIDRValidation.md

@@ -0,0 +1,23 @@
+---
+title: StrictIPCIDRValidation
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: alpha
+    defaultValue: false
+    fromVersion: "1.33"
+---
+Use stricter validation for fields containing IP addresses and CIDR values.
+
+In particular, with this feature gate enabled, octets within IPv4 addresses are
+not allowed to have any leading `0`s, and IPv4-mapped IPv6 values (e.g.
+`::ffff:192.168.0.1`) are forbidden. These sorts of values can potentially cause
+security problems when different components interpret the same string as
+referring to different IP addresses (as in CVE-2021-29923).
+
+This tightening applies only to fields in build-in API kinds, and not to
+custom resource kinds, values in Kubernetes configuration files, or
+command-line arguments.