Add a CLI connection-address override #317

Add a dispatch-cli option for connecting to an explicit address while retaining the hostname from --url for TLS verification and Caddy routing.

Example:

dispatch-cli \
  --url grpc://dispatch.eu-1.staging.api.frequenz.com:443 \
  --resolve fd00:1:0:fffc::110 \
  list <microgrid-id>

This allows staging traffic to use the VPN without changing system DNS or /etc/hosts. The hostname must remain the TLS SNI and HTTP/2 authority; the override must only select the socket connection address.

This depends on frequenz-floss/frequenz-client-base-python#260. Once supported there, expose it through the CLI and an equivalent environment variable, and add CLI tests for IPv4 and IPv6 values.