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/disconnect.go

@@ -0,0 +1,38 @@
+package commands
+
+import (
+	"context"
+
+	"github.com/docker/buildx/monitor/types"
+	"github.com/pkg/errors"
+)
+
+type DisconnectCmd struct {
+	m types.Monitor
+}
+
+func NewDisconnectCmd(m types.Monitor) types.Command {
+	return &DisconnectCmd{m}
+}
+
+func (cm *DisconnectCmd) Info() types.CommandInfo {
+	return types.CommandInfo{HelpMessage: "disconnect a client from a buildx server. Specific session ID can be specified an arg"}
+}
+
+func (cm *DisconnectCmd) Exec(ctx context.Context, args []string) error {
+	target := cm.m.AttachedSessionID()
+	if len(args) >= 2 {
+		target = args[1]
+	}
+	isProcess, err := isProcessID(ctx, cm.m, target)
+	if err == nil && isProcess {
+		if err := cm.m.DisconnectProcess(ctx, target); err != nil {
+			return errors.Errorf("disconnecting from process failed %v", target)
+		}
+		return nil
+	}
+	if err := cm.m.DisconnectSession(ctx, target); err != nil {
+		return errors.Errorf("disconnecting from session failed: %v", err)
+	}
+	return nil
+}