Alertmanager URI might contain basic auth username & password, we should replace password with 'xxx' in logs and and error messages.
Go will still print it in HTTP request errors, but that will be fixed in the next Go release - https://go-review.googlesource.com/c/go/+/102855Fixes#259
For absolute paths we correctly return full decoded path, but for relative paths we can't simply strip file:// prefix as it might leave query args in place. Build absolute path by joining working dir + hostname part + path part.
Add an extra test case for coverage.
This package adds handlers for different URI schemes, name clashes with http.Transport which is now passed around. Rename it to make it more obvious what it does
