implement docker trust as plugin

move the `trust` subcommands to a plugin, so that the subcommands can
be installed separate from the `docker trust` integration in push/pull
(for situations where trust verification happens on the daemon side).

    make binary
    go build -o /usr/libexec/docker/cli-plugins/docker-trust ./cmd/docker-trust

    docker info
    Client:
     Version:    28.2.0-dev
     Context:    default
     Debug Mode: false
     Plugins:
      buildx: Docker Buildx (Docker Inc.)
        Version:  v0.24.0
        Path:     /usr/libexec/docker/cli-plugins/docker-buildx
      trust: Manage trust on Docker images (Docker Inc.)
        Version:  unknown-version
        Path:     /usr/libexec/docker/cli-plugins/docker-trust

    docker trust --help
    Usage:  docker trust [OPTIONS] COMMAND

    Extended build capabilities with BuildKit

    Options:
      -D, --debug   Enable debug logging

    Management Commands:
      key         Manage keys for signing Docker images
      signer      Manage entities who can sign Docker images

    Commands:
      inspect     Return low-level information about keys and signatures
      revoke      Remove trust for an image
      sign        Sign an image

    Run 'docker trust COMMAND --help' for more information on a command.

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

cli/command/commands/commands.go

@@ -18,7 +18,6 @@ import (
 	_ "github.com/docker/cli/cli/command/stack"
 	_ "github.com/docker/cli/cli/command/swarm"
 	_ "github.com/docker/cli/cli/command/system"
-	_ "github.com/docker/cli/cli/command/trust"
 	_ "github.com/docker/cli/cli/command/volume"
 	"github.com/docker/cli/internal/commands"
 	"github.com/spf13/cobra"