Add some docs

Signed-off-by: Mark Anderson <manderson@hashicorp.com>

website/content/docs/connect/config-entries/mesh.mdx

@@ -359,6 +359,20 @@ Note that the Kubernetes example does not include a `partition` field. Configura
         },
       ],
     },
+    {
+      name: 'HTTP',
+      type: 'HTTPConfig: <optional>',
+      description: 'HTTP configuration for the service mesh.',
+      children: [
+        {
+          name: 'SanitizeXForwardedClientCert',
+          yaml: false,
+          type: 'bool: <optional>',
+          description: `Set the envoy forwardClientCertDetails to SANITIZE everywhere. Ordinarily Consul will configure Envoy to
+                        insert x-forwarded-client-cert headers where appropriate. This returns Consul to the pre 1.12.1 behavior`,
+        },
+      ],
+    },
   ]}
 />