Add ecsta cp command

[fujiwara]

This PR adds ecsta cp.

Usage: ecsta cp <src> <dest> [flags]

Copy files from/to a task

Arguments:
  <src>     Source
  <dest>    Destination

Flags:
      --port=12345          port number for file transfer
      --[no-]progress       show progress bar
      --id=STRING           task ID
      --container=STRING    container name
      --family=FAMILY       task definition family name
      --service=SERVICE     ECS service name

Example:

$ ecsta cp /path/to/file.txt _:/tmp/file.txt  # copy file to a task(_ is the selected task)
$ ecsta cp 75dc060ef49b4ba1b2a33581dc5b876f:/tmp/file.txt /path/to/file.txt  # copy file from the task.

ecsta cp copies files from/to a task.

How to work ecsta cp

ecsta cp works as below.

1. ecsta starts a temporary TCP server on the task vie ECS Exec.
   • The server listens on the specified port (default is 12345).
   • tncl is used as the server. It is a tiny TCP server that like nc -l command.
   • The server is terminated when the file transfer is completed.
2. ecsta starts a port forwarding to the temporary server.
3. ecsta connects to the temporary server via the port forwarding.
4. ecsta sends or receives files via the connection.

Requirements:

• The task must have the ECS Exec feature enabled.
• The task must have sh, base64, and chmod commands.