Replace dependency on Java's HttpClient by http4s client

[labra]

I would prefer not to depend on Java's httpClient which depends itself on Java 1.11 and replace it by http4s client.
We used httpClient from java.net.http because it was handy and it allowed us to follow redirects. However, http4s Client also has middleware that supports redirects.

The code to change is in Deref.scala