Add support for Coban Pad 3A

[RyanDam]

Description

Add new keyboard: Coban Pad 3A.
Coban Pad 3A is small macro keyboard with 2 hotswapable button and 1 EC11 rotary encoder

QMK Pull Request

qmk/qmk_firmware#19634

Checklist

• The VIA support for this keyboard is in QMK master already (MANDATORY)
• The VIA definition follows the guide here: https://caniusevia.com/docs/layouts
• I have tested this keyboard definition using VIA's "Design" tab.
• I have tested this keyboard definition with firmware on a device.
• I have assigned alpha keys and modifier keys with the correct colors.
• The Vendor ID is not 0xFEED

[yiancar]

The checklist must be complete to open a PR. As QMK has not been merged into master, I will be closing this PR.
Please write a comment once QMK has been merged and I will reopen it.

[RyanDam]

Hi @yiancar , finally my PR is merged to QMK master. Please have a check on this PR. Thank you in advance.