1153 Add content_guessing optional param to imports API

@Kartones can you please review?
I checked it on staging and it works. Apart from that, there's certain stuff I do prefer to have globally, such as config, logging and metrics. I don't think there's a good reason to not keep them global.

My proposal is to have a global factory/singleton for them. This will unclutter the code (instead of passing this dependencies through N layers). I'm open to discussion