Split off samples into their own repository

[tdaede]

If the samples become much larger, we could split off the large sample files into their own repository so that users of libiamf don't need to fetch them.

[sunghee-hwang]

@jwcullen @yeroro @yilun-zhangs @tdaede,
is it still an open issue or was it already addressed?

[jwcullen]

I added a label to postpone this. It's just a question of how to organize the repos, but I don't think it holds anything back.