Add new file

doc/api/lease4-get.json

+{
+    "name": "lease4-get",
+    "brief": "lease4-get can be used to query the lease database and retrieve existing leases.",
+    "description": "See <xref linkend=\"lease4-get\"/>",
+    "support": [ "kea-dhcp4", "kea-dhcp6" ],
+    "avail": "1.3.0",
+    "hook": "lease_cmds",
+    "cmd-syntax": "{
+    \"command\": \"lease4-get\",
+    \"arguments\": {
+        \"ip-address\": \"192.0.2.1\"
+    }
+}",
+    "resp-syntax": "{
+  \"arguments\": {
+    \"client-id\": \"42:42:42:42:42:42:42:42\",
+    \"cltt\": 12345678,
+    \"fqdn-fwd\": false,
+    \"fqdn-rev\": true,
+    \"hostname\": \"myhost.example.com.\",
+    \"hw-address\": \"08:08:08:08:08:08\",
+    \"ip-address\": \"192.0.2.1\",
+    \"state\": 0,
+    \"subnet-id\": 44,
+    \"valid-lft\": 3600
+  },
+  \"result\": 0,
+  \"text\": \"IPv4 lease found.\"
+}",
+    "resp-comment": "lease4-get returns a result that indicates a result of the operation and lease details, if found. It has one of the following values: 0 (success), 1 (error) or 2 (empty)."
+}
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