feat: add plugin

- add plugin system that request may included to run before do actual request by type.

Signed-off-by: Pakin <pakin.t@forth.co.th>

plugins/plugin.wit

@@ -0,0 +1,10 @@
+package server-m2-dev:plugins;
+
+interface handler {
+    // The plugin takes a message and returns a processed version
+    process-message: func(input: string) -> string;
+}
+
+world plugin-world {
+    export handler;
+}