Update RPMs building for RHEL7

[hecko]

Hello, as a continuing effort to make SEMS a bit more consistent I have patched several files so I can build RPMs in the RHEL7 container image - the Dockefile-rhel7 downloads the sources from github, builds the sems, then producses RPMs which then can be copied from the container image onto the local system.

I have broken some of the conventions in how versioning works for RPMs, but I have not broken anything too significant.

I would like to hear some feedback on this pre-PR diff - Its slightly messy at this stage, but Ill be cleaning it up as I prepare for a PR. The most important bit is the main README section on how to build RPMs and the actual Dockerfile-rhel7

https://github.com/sems-server/sems/compare/master...hecko:sems:fb?expand=1

Other Dockerfiles have not yet been updated (rhel8, rhel9) as Ill be awaiting feedback.