Dockerfile: switch from sudo to doas

Doas a simpler replacement for sudo, which does everything we need. So
switch to doas.
12 jobs for switch-to-doas in 3 minutes and 43 seconds
latest
Status Job ID Name Coverage
  Verify
passed #108322
docker-alpine x86_64
lint

00:00:14

 
  Build
passed #108327
docker-alpine ci-docker-image aarch64
build-aarch64

00:01:37

passed #108328
docker-alpine ci-docker-image armv7
build-armv7

00:01:28

passed #109636
ppc64le ci-docker-image docker-alpine
build-ppc64le

00:01:50

passed #108323
docker-alpine ci-docker-image s390x
build-s390x

00:00:54

passed #108325
docker-alpine ci-docker-image x86
build-x86

00:00:33

passed #108324
docker-alpine ci-docker-image x86_64
build-x86_64

00:00:38

failed #108326
docker-alpine ci-docker-image ppc64le
build-ppc64le

01:00:00

canceled #108469
ppc64le ci-docker-image docker-alpine
build-ppc64le

00:07:04

canceled #108470
docker-alpine ci-docker-image ppc64le
build-ppc64le

00:02:22

failed #108471
ppc64le ci-docker-image docker-alpine
build-ppc64le

01:00:00

failed #108731
docker-alpine ci-docker-image ppc64le
build-ppc64le

01:00:00