WIP: Added RPM packaging for Fedora 35, removed 33/34

NOTE: This MR won't be merged and has been superseded by !1424 (merged) which was based on merging a branch with the changes from this MR (and a number of other subsequent fixes) that had a pkg/ prefix in the branch name in order to run the full packaging pipeline as part of the CI.

Add packaging for Fedora 35. Fedora 33 is now EOL and Fedora 34 will be going EOL soon too. Since there is currently no Fedora packaging enabled, this adds support for Fedora 35 package builds only with a view to also adding support for 36 when that is released soon.

Addresses and closes #281 (closed).