Switch from sudo to doas

Per alpine/tsc#1 (closed), Alpine 3.15 will very likely move sudo from the main repo to community, and switching to doas as its preferred privilege escalation utility.

This shouldn't be hard to do...

• a new profiles/base/3 that installs doas instead of sudo that edge and 3.15 versions pull in
• update /etc/doas.conf to allow passwordless doas for group wheel (similar to what we do for /etc/sudoers)