Add member_leave automod trigger

At least i think so - cant test it until knub changes are done

backend/src/plugins/Automod/triggers/memberLeave.ts

@@ -0,0 +1,20 @@
+import * as t from "io-ts";
+import { automodTrigger } from "../helpers";
+
+export const MemberLeaveTrigger = automodTrigger<unknown>()({
+  configType: t.type({}),
+
+  defaultConfig: {},
+
+  async match({ pluginData, context, triggerConfig }) {
+    if (!context.joined || !context.member) {
+      return;
+    }
+
+    return {};
+  },
+
+  renderMatchInformation({ pluginData, contexts, triggerConfig }) {
+    return "";
+  },
+});