Move the rc framework out of sbin/init into libexec/rc.
The reasons for this are forward looking to pkgbase:
- /sbin/init is a special binary; try not to replace it with every package update because an rc script was touched. (a follow-up commit will make init its own package)
- having rc in its own place will allow more easy replacement of the rc framework with alternatives, such as openrc.
Discussed with: brd (during BSDCam), kmoore
Requested by: cem, bz
PR: 231522
Approved by: re (gjb)