Redirect hostnames to IPs for v2.0.0-beta

[qdm12]

As JSON format

{
  "version": 1,
  "A": {
    "domain.com": ["1.2.3.4"]
  },
}

• Implement at the dial level so it works with both resolvers and servers
• From file redirections.json as bind mount (blocked by rework-config branch)
• Env variable REDIRECTIONS where one can put the entire JSON on a single line (blocked by rework-config branch)

Note: initially proposed in #64

[qdm12]

Done in 156a695 by using MIDDLEWARE_SUBSTITUTER_SUBSTITUTIONS