build: utilize Rollup to bundle action file (#404)

* build: utilize Rollup to bundle file

* build: bundle file with `.mjs` extension

rollup.config.js

@@ -0,0 +1,11 @@
+import { nodeResolve } from "@rollup/plugin-node-resolve";
+import typescript from "@rollup/plugin-typescript";
+
+export default {
+  input: "src/index.ts",
+  output: {
+    dir: "dist",
+    entryFileNames: "[name].mjs",
+  },
+  plugins: [nodeResolve(), typescript()],
+};