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/types/types.go

@@ -0,0 +1,75 @@
+package types
+
+import (
+	"context"
+	"io"
+
+	controllerapi "github.com/docker/buildx/controller/pb"
+	"github.com/docker/buildx/util/progress"
+	"github.com/moby/buildkit/client"
+)
+
+// Monitor provides APIs for attaching and controlling the buildx server.
+type Monitor interface {
+	// Rollback re-runs the interactive container with initial rootfs contents.
+	Rollback(ctx context.Context, cfg controllerapi.InvokeConfig) string
+
+	// Rollback executes a process in the interactive container.
+	Exec(ctx context.Context, cfg controllerapi.InvokeConfig) string
+
+	// Attach attaches IO to a process in the container.
+	Attach(ctx context.Context, pid string)
+
+	// AttachedPID returns ID of the attached process.
+	AttachedPID() string
+
+	// Detach detaches IO from the container.
+	Detach()
+
+	// DisconnectSession finishes the specified session.
+	DisconnectSession(ctx context.Context, targetID string) error
+
+	// AttachSession attaches the monitor to the specified session.
+	AttachSession(ref string)
+
+	// AttachedSessionID returns the ID of the attached session.
+	AttachedSessionID() string
+
+	// Build executes the specified build and returns an ID of the session for debugging that build.
+	Build(ctx context.Context, options controllerapi.BuildOptions, in io.ReadCloser, progress progress.Writer) (ref string, resp *client.SolveResponse, err error)
+
+	// Kill kills the buildx server.
+	Kill(ctx context.Context) error
+
+	// List lists sessions.
+	List(ctx context.Context) (refs []string, _ error)
+
+	// ListPrcesses lists processes in the attached session.
+	ListProcesses(ctx context.Context) (infos []*controllerapi.ProcessInfo, retErr error)
+
+	// DisconnectProcess finishes the specified process.
+	DisconnectProcess(ctx context.Context, pid string) error
+
+	// Inspect returns information about the attached build.
+	Inspect(ctx context.Context) (*controllerapi.InspectResponse, error)
+
+	// Disconnect finishes the attached session.
+	Disconnect(ctx context.Context) error
+}
+
+// CommandInfo is information about a command.
+type CommandInfo struct {
+
+	// HelpMessage is the message printed to the console when "help" command is invoked.
+	HelpMessage string
+}
+
+// Command represents a command for debugging.
+type Command interface {
+
+	// Exec executes the command.
+	Exec(ctx context.Context, args []string) error
+
+	// Info returns information of the command.
+	Info() CommandInfo
+}