feat: s3/transfermanager (v2): round-robin DNS and multi-NIC

[lucix-aws]

Add two functional options to configure http.Transport to do the following:

• round-robin DNS - S3 returns up to 8 DNS records per query, this injects a custom resolver that ensures new connections rotate between these IP addresses.
• multi-value NIC - replaces the underlying DialContext hook with one that cycles between supplied local addresses (NICs).

[Madrigal]

So when we have a cache miss we'll refresh the whole cache? is this what we want?

[lucix-aws]

Not the whole cache? We just re-query for that one host, or am I missing something?

[lucix-aws]

cache is hostname -> []<ip address>

[Madrigal]

You're right, my thinking was that we were storing things like

hostname -> {
  ip1/expiry1
  ip2/expiry2
  ip3/expiry3
}

But we're storing all results of the lookup with the same expiry (since we don't get TTL), so the entries are

hostname -> {
  ip1/expiry1
  ip2/expiry1
  ip3/expiry1
}

Then it doesn't really matter if one expires since all entries from the lookup will expire at the same time. And anyway, anytime we do a lookup for the same hostname, we replace existing values so they effectively always have the same expiry