Add funcitonality to call codegen for several files

[angelrti]

Currently the call to codegen only supports calling IDL 1 by 1. Ideally we could provide al list of files or a folder (preserving the folder structure) to generate code for more than one file. Some initial development of this is done in: https://github.com/rticommunity/dds-datamodels-utils/tree/main/cmake