always pass 'nil' platform to ContainerCreate

Passing nil to ContainerCreate means that the client library will ignore
this arg and not pass it in the list of arguments it submits to the
docker API.

see https://github.com/moby/moby/blob/4c0d75bc8e8311407040ae7c930f5a2c2c9c03aa/client/container_create.go#L49

We don't want to pass the platform arg because we are not using it and
this is the simplest way to ensure continued support of older docker
versions.

agent/dockerclient/dockerapi/docker_client.go

@@ -53,7 +53,6 @@ import (
 	"github.com/docker/docker/api/types/filters"
 	"github.com/docker/docker/api/types/network"
 	"github.com/docker/docker/api/types/volume"
-	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
 const (
@@ -575,7 +574,7 @@ func (dg *dockerGoClient) createContainer(ctx context.Context,
 		return DockerContainerMetadata{Error: CannotGetDockerClientError{version: dg.version, err: err}}
 	}
 
-	dockerContainer, err := client.ContainerCreate(ctx, config, hostConfig, &network.NetworkingConfig{}, &v1.Platform{}, name)
+	dockerContainer, err := client.ContainerCreate(ctx, config, hostConfig, &network.NetworkingConfig{}, nil, name)
 	if err != nil {
 		return DockerContainerMetadata{Error: CannotCreateContainerError{err}}
 	}