Initial version of sphinx documentation and...

- remove ubuntu 21.04 from CI (end of life)
- adjust matrix strategy for clang.yml
- Use lessons learned from RetroArcher on localize.yml, crowdin.yml, and locale.py
- Add end of life comments to Dockerfiles
- Adjust dependency order in Dockerfiles

scripts/Dockerfile-fedora_33

@@ -1,5 +1,8 @@
 FROM fedora:33 AS sunshine-fedora_33
 
+# Fedora 33 end of life is November 2021
+# This file remains for reference only
+
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 RUN dnf -y update && \
     dnf -y group install "Development Tools" && \