Adds Harbor registry V2 API support to retag images to a Harbor destination

[danibaeyens]

Adds an optional flag to select the registry type to be used, using quay.io as a default. Adds Harbor registry V2 API support to retag images to a Harbor destination

[danibaeyens]

I've found that the current logic is too tight to the original quay supported implementation. I wanted to avoid making a whole refactor to correctly use the different types, so, I've just added a similar hook to the existent one for alibaba's. The biggest difference is that for not hardcoding any specific harbor registry (as they are private instances), I've added a flag which helps to select the registry to be used

Fixes #793

[Gacko]

@giantswarm/team-honeybadger Can you please verify if this is still a thing today and close the PR if not? 🙂

[uvegla]

I dont think its relevant anymore, closed it, thanks! 👍🏻 We are also in the process of getting rid of retagger.