feat: add dongle configuration support for splitkb aurora sofle

[sashasimkin]

Added shields splitkb_aurora_sofle_dongle and splitkb_aurora_sofle_peripheral_left to be able to build dongled configuration for this keyboard.

FWIW - the change was tested in my configuration build: https://github.com/sashasimkin/zmk-aurora-sofle-v2/actions/runs/18071698605

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.

[caksoylar]

Hi there, thanks for the PR. I don't believe we intend to accept additional dongle shields for keyboards, and instead encourage folks to follow the recipe at https://zmk.dev/docs/development/hardware-integration/dongle within their own user config if they want to add a dongle to their keyboards that are maintained upstream. I think an exception could be considered if the keyboard ships with a dongle as a product (but that's not the case here AFAIK).