Automate the rotation of issue trage squad (#50526)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50526

This change wants to automate the rotation of the issue triaging squad on Discord.
This is taking us a few minutes every week to rotate the oncall.

This change can save us some time.

The configuration file format is supposed to be like this:
```
{
  "userMap": {
     "discord-username1": "discord-id1",
     "discord-username2": "discord-id2",
     "discord-username3": "discord-id3",
     "discord-username4": "discord-id4"
   },
  "schedule": {
    "date1": ["discord-username1", "discord-username2"],
    "date2": ["discord-username3", "discord-username4"],
  }
}
```

## Changelog
[Internal] - Automate the issue triage oncall rotation

Reviewed By: cortinico

Differential Revision: D72569435

fbshipit-source-id: 435c13350cf503e99302775674e78a20e328e68d