Add release debs/rpms to souffle-lang.github.io/ppa

[mmcgr]

• Moves deb files to souffle-lang repo after building and updates release data.
• Fixes missing dependency building arch packages.
• Replaces EOL centos8 with oraclelinux8. There may be a better alternative?
• Remove EOL Ubuntu 2010
• Remove packagecloud use.
• Packaging is no longer dependent on successful builds - this allows re-running to fix transient issues.
• RPM repo added for Fedora 34 and OracleLinux 8 (should be compatible with any of the CentOS8 'clones'
• RPM package description fixed (CPack variable use is quirky ...)

Deb files are kept in stable. If there are any distro-specific quirks then this should be expanded.

[codecov]

Codecov Report

Merging #2261 (7a15b74) into master (418a194) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2261      +/-   ##
==========================================
- Coverage   75.15%   75.12%   -0.03%     
==========================================
  Files         455      455              
  Lines       28465    28465              
==========================================
- Hits        21392    21385       -7     
- Misses       7073     7080       +7     

Impacted Files	Coverage Δ
src/include/souffle/profile/ProfileEvent.h	92.85% <0.00%> (-5.11%)	⬇️
src/include/souffle/datastructure/BTree.h	96.63% <0.00%> (-0.43%)	⬇️

[b-scholz]

Thanks for the contribution!