[pluggable monitor] Add monitor --describe command

[cmaglie]

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• The PR has no duplicates (please search among the Pull Requests
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• The PR follows
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• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
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• What kind of change does this PR introduce?
  This PR implements the monitor --describe command and set up the scaffolding for the future monitor command.

$ arduino-cli monitor
Error: required flag(s) "port" not set
Usage:
  arduino-cli monitor [flags]

Esempi:
  arduino-cli monitor -p /dev/ttyACM0
  arduino-cli monitor -p /dev/ttyACM0 --describe

Flags:
      --describe                     Show all the settings of the communication port.
      --discovery-timeout duration   Max time to wait for port discovery, e.g.: 30s, 1m (default 5s)
  -h, --help                         help for monitor
  -p, --port string                  Upload port address, e.g.: COM3 or /dev/ttyACM2
  -l, --protocol string              Upload port protocol, e.g: serial

Global Flags:
      --additional-urls strings   Comma-separated list of additional URLs for the Boards Manager.
      --config-file string        The custom config file (if not specified the default will be used).
      --format string             The output format for the logs, can be: text, json (default "text")
      --log-file string           Path to the file where logs will be written.
      --log-format string         The output format for the logs, can be: text, json
      --log-level string          Messages with this level and above will be logged. Valid levels are: trace, debug, info, warn, error, fatal, panic
      --no-color                  Disable colored output.
  -v, --verbose                   Print the logs on the standard output.

$ arduino-cli monitor -p /dev/ttyACM0 --describe
ID        Setting   Default Values                                                                                                              
baudrate  Baudrate  9600    300, 600, 750, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 500000, 921600, 1000000, 2000000
bits      Data bits 8       5, 6, 7, 8, 9                                                                                                       
parity    Parity    None    None, Even, Odd, Mark, Space                                                                                        
stop_bits Stop bits 1       1, 1.5, 2                                                                                                           

$ arduino-cli monitor -p /dev/ttyACM0
Monitor functionality not yet implemented
$