Add new file

doc/api/dhcp-enable.json

+{
+    "name": "dhcp-enable",
+    "brief": "The dhcp-enable command globally enables the DHCP service.",
+    "description": "See <xref linkend=\"command-dhcp-enable\"/>",
+    "support": [ "kea-dhcp4", "kea-dhcp6" ],
+    "avail": "1.4.0",
+    "cmd-syntax": "{
+    \"command\": \"dhcp-enable\"
+}",
+}
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