systemd target monitoring enable

[Andrew Geissler]

systemd target monitoring and error generation is coming soon to phosphor.

The design doc is here:
  https://github.com/openbmc/docs/blob/master/designs/target-fail-monitoring.md

The code implementation series is here:
  https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-state-manager/+/24136/

The bitbake commit that will enable it is here:
  https://gerrit.openbmc-project.xyz/c/openbmc/meta-phosphor/+/24430

The current plan is that if you include bmc-state-mgmt from the
phosphor-state-manager repo then you will get this new function by default.
If you'd rather it be an opt-in then feel free to reply here or on that last
review linked above.

Andrew