Convert .golangci.yml to the v2 layout: linters-settings and
issues.exclude-use-default were rejected by the v2 schema, so the lll,
funlen, cyclop, and dupl settings were never applied. Disable
exhaustruct_v5 (the newer major version of the already-disabled
exhaustruct) and the deprecated gomodguard. Pin the golangci-lint image
at v2.15.0 in the Makefile and Dockerfile.
Bring back the in-progress viper and go-homedir configuration loading
from the original root command as a persistent pre-run on the root
command, with a --config flag and a config line in sutil info. Restore
the exported main.Version with a nolint directive instead of renaming
it. Export CGO_ENABLED=0 from the Makefile, drop -race from make test,
and remove the C toolchain from the Docker builder stage.
sneak