Extract the Google Translation functionality to an adapter based lookup

[erral]

Currently plone.app.multilingual supports connecting to Google Cloud Translation API to automatically translate content when translating a page in Plone.

Now that AI and machine translation quality is so good and there are so many services, I think that it would be nice to build a generic solution to achieve this, and let addon creators manage the connection to external services in an easier way.

Right now, if one wants to use some other service, needs to override a view where the 95% of the code will be copied over

I propose to change to an adapter based lookup, which will allow addons to register their own adapter (possibly with control panels to save API keys or endpoints) to do the translation work.