feat(medusa-plugin-mailchimp): Migrate to TS + add update endpoint (#4040)

* - Refactored the .js files to .ts files
- Added typing
- Used 'WrapHandler' util instead of specific middleware in plugin
- Added additional PUT method to the /mailchimp/subscribe endpoint.
- Updated documentation where relevant.

* Added changeset

* Updated yarn.lock

* Used camelcase for method args in services/mailchimp.ts

---------

Co-authored-by: Tom Rupke <tom@adapptive.nl>
Co-authored-by: Oliver Windall Juhl <59018053+olivermrbl@users.noreply.github.com>

packages/medusa-plugin-mailchimp/tsconfig.json

@@ -0,0 +1,27 @@
+{
+  "compilerOptions": {
+    "lib": ["es5", "es6"],
+    "target": "esnext",
+    "allowJs": true,
+    "esModuleInterop": false,
+    "module": "commonjs",
+    "moduleResolution": "node",
+    "emitDecoratorMetadata": true,
+    "experimentalDecorators": true,
+    "skipLibCheck": true,
+    "skipDefaultLibCheck": true,
+    "declaration": false,
+    "sourceMap": false,
+    "outDir": "./dist",
+    "rootDir": "src",
+    "baseUrl": "src"
+  },
+  "include": ["src"],
+  "exclude": [
+    "dist",
+    "./src/**/__tests__",
+    "./src/**/__mocks__",
+    "./src/**/__fixtures__",
+    "node_modules"
+  ]
+}