bake: fix compose consistency check

[crazy-max]

fixes #1172

Consistency check added in #87 is already handled by the library: https://github.com/compose-spec/compose-go/blob/c45b40b31e66dbc3966642803d133bba33680b21/loader/validate.go#L31-L33

Since we have moved to the compose-go library, we can skip the consistency check, remove the dup check in bake as well and use our own "less-strict" consistency check in bake to be aligned with the HCL format:

# docker-compose.yml
services:
  test:
    build:
      context: .
      tags:
        - docker.io/username/webapp:latest
    entrypoint: echo 1

# docker-compose.prod.yml
services:
  test:
    entrypoint: echo 2

$ docker buildx bake -f docker-compose.yml test --print
{
  "group": {
    "default": {
      "targets": [
        "test"
      ]
    }
  },
  "target": {
    "test": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": [
        "docker.io/username/webapp:latest"
      ]
    }
  }
}

$ docker buildx bake -f docker-compose.prod.yml test --print
{
  "group": {
    "default": {
      "targets": [
        "test"
      ]
    }
  },
  "target": {
    "test": {
      "context": ".",
      "dockerfile": "Dockerfile"
    }
  }
}

$ docker buildx bake -f docker-compose.yml -f docker-compose.prod.yml test --print
{
  "group": {
    "default": {
      "targets": [
        "test"
      ]
    }
  },
  "target": {
    "test": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": [
        "docker.io/username/webapp:latest"
      ]
    }
  }
}

Signed-off-by: CrazyMax [email protected]