Prompt to add keyboard to build matrix after creating new keyboard

[joelspadin]

After running zmk keyboard new, we should ask if you want to add the new keyboard to the build matrix.

This should run through the same logic as zmk keyboard add, so if you created a new shield, it should ask which controller board to use. This will require adding another input to shield creation to select the interconnect, as the current templates assume pro_micro, and we need to know which interconnect is used before selecting a controller board.

We should also add a way to mark which templates are actually keyboards. If we add a template for a controller board, that should not be added to the build matrix on its own.

[caksoylar]

This seems resolved now by #51.

[joelspadin]

Agreed.