docs: add sentinel command example for RHEL family

[khuedoan]

Add example for RHEL.

Fixes #498

[jackfrancis]

Has there been thorough testing that this works without escaping quotes? This is definitely valid yaml, but the dispatch of this string includes a few stops along the way until it gets to the actual host OS as a command string, wanna make sure we're good here.

Thanks!

[khuedoan]

Yes, Helm still creates the same output YAML with or without quotes:

# ...
          command:
            - /usr/bin/kured
          args:
            - --ds-name=release-name-kured
            - --ds-namespace=default
            - --reboot-sentinel-command=sh -c "! needs-restarting --reboothint"
            - --reboot-command=/bin/systemctl reboot
            - --log-format=text
# ...

I've tested both in my homelab

[jackfrancis]

/lgtm

[chadswen]

Looks great. This will save people some trial and error time.

Not to derail, but has anyone else tried something like --reboot-sentinel-command=sh -c "[ -f /var/run/reboot-required ] || ( [ -x /usr/bin/needs-restarting ] && ! needs-restarting -r )" to support clusters with a mix of both Red Hat and Debian family nodes? Would that be worth including here for better compatibility?

[khuedoan]

I don't have a cluster with mixed distros so I can't test that, therefore it won't be included in this PR, but in theory it should work.

[ghost]

while i single quoted the string for safety the command worked perfectly for me on fedora 35