Add new file

doc/api/lease6-update.json

+{
+    "name": "lease6-update",
+    "brief": "The lease6-update command can be used to update existing leases.",
+    "description": "See <xref linkend=\"lease6-update\"/>",
+    "support": [ "kea-dhcp4", "kea-dhcp6" ],
+    "avail": "1.3.0",
+    "hook": "lease_cmds",
+    "cmd-syntax": "{
+  \"command\": \"lease6-update\",
+  \"arguments\": {
+    \"ip-address\": \"2001:db8::1\",
+    \"duid\": \"88:88:88:88:88:88:88:88\",
+    \"iaid\": 7654321,
+    \"hostname\": \"newhostname.example.org\",
+    \"subnet-id\": 66,
+    \"force-create\": false
+  }
+}
+",
+}
\ No newline at end of file