Update google-calendar recipe to load external scripts to fix CSP error

[vraravam]

Pre-flight Checklist

Please ensure you've completed all of the following.

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.

Description of Change

Based on https://github.com/ferdium/ferdium-app/issues/1086\#issuecomment-1656926137, fixed google calendar recipe to load the external css.

[mcmxcdev]

Veriified locally that it works:

• went to /recipes folder inside ferdium-app and applied the same changes as here
• ran pnpm package in recipes folder
• started ferdium-app locally with pnpm debug
• waited until I was told that services have been updated by prompt
• reloaded google-calendar service and dark mode works again

---

I think though that dark mode is always on now with how its set up. We would need to do something like in https://github.com/ferdium/ferdium-recipes/blob/main/recipes/android-messages/webview.js#L43-L47 I assume to be able to toggle it.

[mcmxcdev]

I updated the code to be able to toggle between rather than always have dark mode enforced in 23bf649 (#402)

Also verified that the correct theme mode is chosen initially when reloading the service (tested once with dark mode enabled, once disabled)

Here is a video showcasing it working:

Screencast.from.2023-08-07.19-28-35.webm

[lukassr]

It is important to note that, if enabling Dark Mode in an existing Google Calendar service does not work, you may need to delete it and create a new one.