The controller's tools can set an assignment's settings

Per-machine and mesh-wide settings could be set only from the
controller's command line. The settings verb runs settings set|clear,
passing the values inline, which the command now accepts as well as a
file (novox/hq issue 198).

cmd/mesh-controller/seatverbs_test.go

@@ -73,6 +73,22 @@ func TestRotateTakesAProvisionOrAnOwnSecret(t *testing.T) {
 	}
 }
 
+// `settings` is `settings set|clear` at a shell, with the values passed inline (novox/hq issue 198).
+func TestSettingsSetsOrClearsALayer(t *testing.T) {
+	argv, err := argvFor("settings", map[string]any{"module": "dnsmasq", "values": `{"a":1}`, "node": "ace"})
+	if err != nil || strings.Join(argv, " ") != `settings set dnsmasq {"a":1} --node ace` {
+		t.Fatalf("set on a machine: %v %v", argv, err)
+	}
+	argv, _ = argvFor("settings", map[string]any{"module": "dnsmasq", "clear": "true"})
+	if strings.Join(argv, " ") != "settings clear dnsmasq" {
+		t.Fatalf("clear for the mesh: %v", argv)
+	}
+	argv, _ = argvFor("settings", map[string]any{"module": "dnsmasq"})
+	if strings.Join(argv, " ") != "settings set dnsmasq" {
+		t.Fatalf("a set with no values falls to the command's usage: %v", argv)
+	}
+}
+
 // `issue` is `module issue` at a shell: the module and the machine, and nothing that would push. A
 // module's bus account was mintable only from the controller's command line, so an agent working
 // through the tools could not finish a rollout that gave a module one (novox/hq issue 191).