[nit feature] show configured options when running pomodoro

[24seconds]

Description

When the pomodoro is running, sometimes user may(?) want to know what was the configuration.
To solve this curiosity, it would be nice to provide this

# IPC mode
> pomodoro config list 

# standalone mode
> config list

# expected output sample
[2023-03-28T11:56:07Z INFO  pomodoro::configuration]
    config flag result!
    ┌────┬─────────────────────┬───────────────────────────────────┐
    │ ok │ desc                │ reason                            │
    ├────┼─────────────────────┼───────────────────────────────────┤
    │ O  │ no config err       │                                   │
    ├────┼─────────────────────┼───────────────────────────────────┤
    │ X  │ slack_channel       │ can not find slack config in json │
    ├────┼─────────────────────┼───────────────────────────────────┤
    │ X  │ slack_token         │ can not find slack config in json │
    ├────┼─────────────────────┼───────────────────────────────────┤
    │ O  │ discord_webhook_url │                                   │
    └────┴─────────────────────┴───────────────────────────────────┘

[24seconds]

If it is too much then it's good to separate this issue into two

1. implement config list in standalone mode
2. implement config list for IPC mode