nmcli-agent, nmcli-radio: add page (#7863)

pages/linux/nmcli-agent.md

@@ -0,0 +1,17 @@
+# nmcli agent
+
+> Run nmcli as a NetworkManager secret agent or polkit agent.
+> See also: `nmcli radio`.
+> More information: <https://networkmanager.dev/docs/api/latest/nmcli.html>.
+
+- Register nmcli as a secret agent and listen for secret requests:
+
+`nmcli agent secret`
+
+- Register nmcli as a polkit agent and listen for authorization requests:
+
+`nmcli agent polkit`
+
+- Register nmcli as a secret agent and a polkit agent:
+
+`nmcli agent all`