`install_runner_prerequisites` doesn't ensure chrony is installed

Reproduced by trying to run a dev cluster for the first time since #3825 landed (wow has it been a while!).

The cluster didn't come up on first boot; sled agent logs suggested that the issue was that chronyc wasn't on the path. Uninstalling and running pkg install chrony was enough to get me past that failure mode, so I suspect we need to add this to the list of packages in install_runner_prerequisites.sh.

This was not enough to get me up and running; after this chronyc ran in the NTP zone but consistently failed with 506 Cannot talk to daemon errors. I didn't have chronyd running anywhere (in the GZ or otherwise) when I first tried this, so I uninstalled, tried to start the daemon, and reinstalled, but that didn't seem to fix it, so I ultimately decided to get unblocked by setting skip_timesync back to true. This needs more investigation and possibly a separate issue.

Open install_runner_prerequisites.sh and compare its package list with the prerequisites needed for a first dev-cluster boot. Reproduce the missing-chronyc failure if possible, then verify that installing the prerequisites provides chronyc; the later 506 Cannot talk to daemon failure may require separate investigation.