Add "platform" column to docker ps

With this change:

    docker create armhf/hello-world
    docker create hello-world

    docker ps -a
    CONTAINER ID   IMAGE               PLATFORM      COMMAND    CREATED          STATUS                      PORTS     NAMES
    a020fcae5f4d   hello-world         linux/amd64   "/hello"   5 seconds ago    Exited (0) 3 seconds ago              vigorous_yalow
    499a18874987   armhf/hello-world   linux/arm64   "/hello"   58 seconds ago   Exited (0) 57 seconds ago             hardcore_brown

    docker ps -a --format=raw
    container_id: a020fcae5f4d
    image: hello-world
    platform: linux/amd64
    command: "/hello"
    created_at: 2021-07-05 07:08:19 +0000 UTC
    state: exited
    status: Exited (0) About an hour ago
    names: vigorous_yalow
    labels:
    ports:

    container_id: 499a18874987
    image: armhf/hello-world
    platform: linux/arm64
    command: "/hello"
    created_at: 2021-07-05 07:07:26 +0000 UTC
    state: exited
    status: Exited (0) About an hour ago
    names: hardcore_brown
    labels:
    ports:

    docker ps -a --format '{{json .}}' | jq .
    {
      "Command": "\"/hello\"",
      "CreatedAt": "2021-07-05 07:08:19 +0000 UTC",
      "ID": "a020fcae5f4d",
      "Image": "hello-world",
      "Labels": "",
      "LocalVolumes": "0",
      "Mounts": "",
      "Names": "vigorous_yalow",
      "Networks": "bridge",
      "Platform": "linux/amd64",
      "Ports": "",
      "RunningFor": "52 seconds ago",
      "Size": "0B (virtual 13.3kB)",
      "State": "exited",
      "Status": "Exited (0) 51 seconds ago"
    }
    {
      "Command": "\"/hello\"",
      "CreatedAt": "2021-07-05 07:07:26 +0000 UTC",
      "ID": "499a18874987",
      "Image": "armhf/hello-world",
      "Labels": "",
      "LocalVolumes": "0",
      "Mounts": "",
      "Names": "hardcore_brown",
      "Networks": "bridge",
      "Platform": "linux/arm64",
      "Ports": "",
      "RunningFor": "About a minute ago",
      "Size": "0B (virtual 1.64kB)",
      "State": "exited",
      "Status": "Exited (0) About a minute ago"
    }

To be discussed: what should the presentation be of platform if an "os variant" is present?

For example (from `docker manifest inspect hello-world`);

```json
{
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "size": 1125,
  "digest": "sha256:90e120baffe5afa60dd5a24abcd051db49bd6aee391174da5e825ee6ee5a12a0",
  "platform": {
    "architecture": "amd64",
    "os": "windows",
    "os.version": "10.0.17763.1999"
  }
}
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

cli/command/formatter/container.go

@@ -14,7 +14,7 @@ import (
 )
 
 const (
-	defaultContainerTableFormat = "table {{.ID}}\t{{.Image}}\t{{.Command}}\t{{.RunningFor}}\t{{.Status}}\t{{.Ports}}\t{{.Names}}"
+	defaultContainerTableFormat = "table {{.ID}}\t{{.Image}}\t{{.Platform}}\t{{.Command}}\t{{.RunningFor}}\t{{.Status}}\t{{.Ports}}\t{{.Names}}"
 
 	namesHeader      = "NAMES"
 	commandHeader    = "COMMAND"
@@ -42,6 +42,7 @@ func NewContainerFormat(source string, quiet bool, size bool) Format {
 		}
 		format := `container_id: {{.ID}}
 image: {{.Image}}
+platform: {{.Platform}}
 command: {{.Command}}
 created_at: {{.CreatedAt}}
 state: {{- pad .State 1 0}}
@@ -92,6 +93,7 @@ func NewContainerContext() *ContainerContext {
 		"ID":           ContainerIDHeader,
 		"Names":        namesHeader,
 		"Image":        ImageHeader,
+		"Platform":     PlatformHeader,
 		"Command":      commandHeader,
 		"CreatedAt":    CreatedAtHeader,
 		"RunningFor":   runningForHeader,
@@ -294,6 +296,12 @@ func (c *ContainerContext) Networks() string {
 	return strings.Join(networks, ",")
 }
 
+// Platform returns formatted string representing the container image's
+// platform (e.g. linux/arm/v7).
+func (c *ContainerContext) Platform() string {
+	return c.c.Platform.String()
+}
+
 // DisplayablePorts returns formatted string representing open ports of container
 // e.g. "0.0.0.0:80->9090/tcp, 9988/tcp"
 // it's used by command 'docker ps'

cli/command/formatter/custom.go

@@ -16,6 +16,7 @@ const (
 	StatusHeader       = "STATUS"
 	PortsHeader        = "PORTS"
 	ImageHeader        = "IMAGE"
+	PlatformHeader     = "PLATFORM"
 	ContainerIDHeader  = "CONTAINER ID"
 )