Merge pull request #31531 from poettering/verity-userspace-optional

dissect: make use of userspace verity keyring optional

diff --cc docs/ENVIRONMENT.md
Simple merge

diff --cc man/kernel-command-line.xml
Simple merge

diff --cc src/shared/dissect-image.c
Simple merge

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