systemd: relaunch sssd after unclean exit

[Squiddim]

This PR aims to fix #6219 by swapping the restart policy of the sssd systemd unit back to on-failure.

The change to Restart=on-abnormal was introduced in Commit a049ac7 to fix an infinite loop on system boot caused by misconfiguration (see #5753 / https://bugzilla.suse.com/show_bug.cgi?id=1188999).

While this fixed their issue, I'd argue that the StartLimit settings introduced alongside it should accomplish the goal of avoiding an infinite loop in most scenarios:

     StartLimitIntervalSec=50s
     StartLimitBurst=5

I believe that the issues fixed (#6219) by setting the restart policy back to on-failure take precedence over the edge cases where sssd could inhibit system boot when sssd/subsystems are too slow to trigger the StartLimit.

[gemini-code-assist]

Code Review

The pull request changes the systemd Restart policy for sssd from on-abnormal to on-failure. This aims to address issue #6219 by allowing sssd to restart in more failure scenarios, including watchdog kills. The author acknowledges that on-abnormal was previously introduced to prevent infinite restart loops due to misconfiguration, and argues that existing StartLimit directives should mitigate this risk. However, there's a potential for the original issue to re-emerge in certain edge cases if the StartLimit configuration is not fully comprehensive.

[gemini-code-assist]

The change from Restart=on-abnormal to Restart=on-failure reintroduces the risk of an infinite restart loop on system boot due to misconfiguration, which on-abnormal was specifically intended to prevent (as noted in the PR description regarding #5753). While StartLimitIntervalSec and StartLimitBurst are in place, the description mentions "most Scenarios" and "Edge Cases where sssd could inhibit a System boot". This suggests that these limits might not fully mitigate the original problem in all situations. Re-evaluating the StartLimit values or considering a more robust mechanism to prevent boot inhibition under misconfiguration is crucial for system stability.