compose: support healthcheck field in service config

[opjt]

• related issue : nerdctl compose should support djocker compose service health check #4709

Summary

services.<SERVICE>.healthcheck was listed as unimplemented — this PR wires it up.

compose-go already parses the healthcheck block, so this is mostly connecting
it to the existing --health-* flags in serviceparser.

Limitations:

• CMD exec form is converted to CMD-SHELL since --health-cmd always stores the command as CMD-SHELL (see withHealthcheck in pkg/cmd/container/create.go)
• start_interval is not supported — I plan to work on this after this PR is merged.

Test plan

services:
  web:
    image: nginx:alpine
    healthcheck:
      test: ["CMD-SHELL", "curl -f http://localhost"]
      interval: 10s
      timeout: 5s
      retries: 3
      start_period: 2s

  nerdctl compose up -d
  nerdctl inspect <container-name> | grep health