Add needrestart_info.py to monitore needrestart.

[RomainMou]

Hi,

I've made a small script to retrieve some metrics from needrestart, and perhaps it could be useful for others?

The script runs needrestart -b (batch mode), parses the output, and displays some metrics. It looks like this:

# HELP needrestart_timestamp information about the version and when it was last run
# TYPE needrestart_timestamp gauge
needrestart_timestamp{version="3.5"} 1.702655157e+09
# HELP needrestart_kernel_status information about the kernel status
# TYPE needrestart_kernel_status gauge
needrestart_kernel_status{current="5.10.0-26-amd64",expected="5.10.0-26-amd64"} 1.0
# HELP needrestart_services_count number of services requiring a restart
# TYPE needrestart_services_count gauge
needrestart_services_count 0.0
# HELP needrestart_containers_count number of containers requiring a restart
# TYPE needrestart_containers_count gauge
needrestart_containers_count 0.0
# HELP needrestart_sessions_count number of sessions requiring a restart
# TYPE needrestart_sessions_count gauge
needrestart_sessions_count 0.0

[RomainMou]

Hello @funkyfuture, thanks for all your feedback, they are very appreciate for a beginner like me.
I've try to take all of them into account.

[funkyfuture]

lgtm, i've been using it for some weeks now.

[RomainMou]

Is there anything missing to merge this PR? Anything I can do?

[dswarbrick]

Please also check that your metric names conform to the Prometheus best practice guide: https://prometheus.io/docs/practices/naming/

[calestyo]

Just for the records: There's has also been something coded in needrestart itself: liske/needrestart#291