Merge pull request #14390 from poettering/gpt-var-tmp

introduce GPT partition types for /var and /var/tmp and support them for auto-discovery

diff --cc TODO
Simple merge

diff --cc man/systemd-nspawn.xml
Simple merge

diff --cc man/systemd.exec.xml
Simple merge

diff --cc src/core/execute.c
Simple merge

diff --cc src/gpt-auto-generator/gpt-auto-generator.c
Simple merge

diff --cc src/nspawn/nspawn.c
Simple merge