monitor: Move commands to a separated package

This commit moves monitor commands to `monior/commands` package.
Commands still need access to the `monitor` object and buildx controller so this
commit enables this via `Monitor` interface stored in `monitor/types`.

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

monitor/commands/rollback.go

@@ -0,0 +1,43 @@
+package commands
+
+import (
+	"context"
+	"fmt"
+	"io"
+
+	controllerapi "github.com/docker/buildx/controller/pb"
+	"github.com/docker/buildx/monitor/types"
+)
+
+type RollbackCmd struct {
+	m types.Monitor
+
+	invokeConfig controllerapi.InvokeConfig
+	stdout       io.WriteCloser
+}
+
+func NewRollbackCmd(m types.Monitor, invokeConfig controllerapi.InvokeConfig, stdout io.WriteCloser) types.Command {
+	return &RollbackCmd{m, invokeConfig, stdout}
+}
+
+func (cm *RollbackCmd) Info() types.CommandInfo {
+	return types.CommandInfo{HelpMessage: "re-runs the interactive container with initial rootfs contents"}
+}
+
+func (cm *RollbackCmd) Exec(ctx context.Context, args []string) error {
+	cfg := cm.invokeConfig
+	if len(args) >= 2 {
+		cmds := args[1:]
+		if cmds[0] == "--init" {
+			cfg.Initial = true
+			cmds = cmds[1:]
+		}
+		if len(cmds) > 0 {
+			cfg.Entrypoint = []string{cmds[0]}
+			cfg.Cmd = cmds[1:]
+		}
+	}
+	id := cm.m.Rollback(ctx, cfg)
+	fmt.Fprintf(cm.stdout, "Interactive container was restarted with process %q. Press Ctrl-a-c to switch to the new container\n", id)
+	return nil
+}