feat: implement optional group property for Preferences API

[kumibrr]

Feature Request

Plugin

@capacitor/preferences

Description

Currently, all preferences share a global flat namespace configured globally by the configure({group}) API.

This makes it difficult to manage separate logical buckets (e.g., App Settings vs. User Preferences) or clear specific sets of data without affecting others, especially during app initialization.

Platform(s)

Android, iOS, Web

Preferred Solution

I'd like to add an optional group: string property in GetOptions, SetOptions, RemoveOptions.
Creating an optional argument KeysOptions with group: string.

This property would be set to the current configured group by default.