Ignore `Multiaddr`s with DNS protocol components.

Issue #5756 recommends not resolving DNS names to prevent leaking DNS
configuration. In order to achieve this the following modifications are
applied:

- `Multiaddr` values received via libp2p-identify are ignored if they
  contain a DNS protocol component.
- In `Discovery` `Multiaddr` values with a DNS protocol component are
  not inserted into the DHT unless the command-line option `discover-local`
  is present which allows non-global IP addresses and DNS names in the DHT
  and is meant for site-local deployments.
- In `authority-discovery` we filter `Multiaddr` values received from
  the DHT and ignore those with and DNS protocol component.