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>

.changeset/lovely-readers-live.md

@@ -0,0 +1,5 @@
+---
+"medusa-plugin-mailchimp": patch
+---
+
+feat(medusa-plugin-mailchimp): Added PUT method for the /mailchimp/subscribe endpoint.