Add new file

doc/api/lease4-get-all.json

+{
+    "name": "lease4-get-all",
+    "brief": "lease4-get-all is used to retrieve all IPv4 leases or all leases for the specified set of subnets.",
+    "description": "See <xref linkend=\"lease4-get-all\"/>",
+    "support": [ "kea-dhcp4", "kea-dhcp6" ],
+    "avail": "1.4.0",
+    "hook": "lease_cmds",
+    "cmd-syntax": "{
+    \"command\": \"lease4-get-all\"
+}",
+    "cmd-comment": "The lease4-get-all command may result in very large responses.",
+}
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