Support extra_hosts on pre_start

[ArtuoS]

What I did

Fixes #13939.

pre_start hooks run as ephemeral containers with their own HostConfig, but the configuration was built with only four fields (AutoRemove, Privileged, VolumesFrom, NetworkMode), omitting ExtraHosts entirely. This meant custom host mappings defined on the service were invisible inside pre_start containers, even though they were correctly applied to the main service containers.

This PR propagates service.ExtraHosts into the pre_start container's HostConfig, matching the behavior of regular containers created via getCreateConfigs().

Location	Change
pkg/compose/pre_start.go — createPreStartContainer	Set ExtraHosts: service.ExtraHosts.AsList(":") on the hook container's HostConfig
pkg/compose/pre_start_test.go	New TestPreStart_ExtraHostsPassedToContainer verifying the host mapping is forwarded

Scope

Only ExtraHosts is in scope. Other HostConfig fields (e.g. DNS, CapAdd, SecurityOpt) are not propagated to pre_start containers and can be addressed separately if needed.

How to test manually

services:
  test:
    image: busybox
    extra_hosts:
      - "somehost:162.242.195.82"
    pre_start:
      - command: cat /etc/hosts
    command: cat /etc/hosts

$ docker compose up
test pre_start[0] -> | 127.0.0.1	localhost
test pre_start[0] -> | 162.242.195.82	somehost   ← now visible
test-1               | 162.242.195.82	somehost

[ndeloof]

This assumes we want the pre_start to inherit config from service, which must be debated (what should be inherited? What should not? How to override?)