New feature: JSON reminder entry, as an independent command to add an entry

[mgiugliano]

Enabling setting the "recurring" properties of a reminder, and future extension, this pull requests adds a new command: add-json.

This receives an input JSON-formatted string, containing all the reminders properties (including the listName).

json_string='{
  "title": "Buy groceries",
  "notes": "Milk, eggs, bread, cheese",
  "dueDate": "2025-02-15T10:24:00Z",
  "priority": "medium",
  "listName": "Groceries",
  "recurring": "weekly",
}'``` 

One could then invoke reminders simply as:

$ reminders add-json $json_string

In this way, simple shell aliases or other programmatic means can feed other properties to the reminder at the time of its creation. The ```format``` flag can be still specified (controlling the output of reminders), but I did not test it thoroughly.

Note I have explored startingDate, url, and other properties/attributes but failed to make them all work. The argument of "recurring" could definitely be improved. It currently accepts: daily, weekly, monthly, yearly. Maybe this could be of help to other people.

Thanks for your excellent work and for (indirectly) showing me "swift", which I am still a complete noob about. :)