Unmarshal URL's with urls.redacted

[roidelapluie]

trafficstars

I propose that since go 1.15 supports url.Redacted, we make used of it while unmarshaling urls.

This could be done my adding a URL wrapper in this repo.

https://github.com/golang/go/issues/34855

[brian-brazil]

We provide a way that occludes secrets for basic auth, do we really need this? Also the way Go occludes is different to the way we do it in terms of placeholder, which would be confusing.

[roidelapluie]

We do not provide a way to do Proxy Authentication.

[brian-brazil]

Then that is something we should discuss, I think there's an issue for it lying about somewhere.

[simonpasquier]

It was https://github.com/prometheus/common/issues/128