Add Sparkfun Thing Plus Matter - MGM240P support

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Configuration

Operating system: Windows 10

PlatformIO Version (platformio --version): PlatformIO Core, version 6.1.13

Description of problem

Arduino, Sparkfun and Silicon Labs have a new Matter project: https://github.com/SiliconLabs/arduino/tree/main/libraries/Matter

I would like to use VS Code to program the Sparkfun Things Plus Matter ( Model DEV-20270 ) dev board using the Silicon Labs developed Arduino Libraries. (Arduino compiling is painfully slow.)
https://www.sparkfun.com/products/20270

I cannot find this board in the Platformio device list.

Steps to Reproduce

1. In VS Code - Platformio select 'Import Arduino Project'
2. Attempt to find the Sparkfun Thing Plus Matter - MGM240P

Actual Results

Product is not listed.

Expected Results

Product listed and Platformio able to use the Matter libraries from Arduino

Additional info

This board is available in Arduino - board info is from https://siliconlabs.github.io/arduino/package_arduinosilabs_index.json
The board comes with all of the appropriate Matter Arduino libraries for this Sparkfun and the Silicon Labs xG24 Explorer Kit dev boards.

Start with the VS Code PlatformIO “Import Arduino Project” flow and compare the missing Sparkfun Thing Plus Matter - MGM240P against the Silicon Labs Arduino package index linked in the issue. Done means the board appears in the PlatformIO device list and can use the referenced Matter Arduino libraries.