Make sure Dockerfiles work as intended

[Tjzabel]

The RPM and ISO building Dockerfiles were added into this repository, but have not been properly tested.

Before we can make use of docker to help with the CI, we need to test docker manually.
I believe there is still a small issue with the ISO Dockerfile (I have the issue logged somewhere) before it can work as expected.

RPM Dockerfile should be working, but needs to be further tested.

[Tjzabel]

Update

ISO Dockerfile works almost as expected. There is a seemingly small issue at the very end of the ISO building process that makes the process fail.

At this point, since we know the ISO Dockerfile is for the most part working, I am going to hold off on further ISO testing until we have TigerOS 29 up and running.