Add support to specify path to sys/proc etc.

[perosb]

When running in k8s f.ex., the /sysand /proc must be mounted from the host.

In node_exporter I can specify f.ex:

        - --path.procfs=/host/proc
        - --path.sysfs=/host/sys
        - --path.rootfs=/host/root

Can this be added to rpi_exporter too?

time="2023-11-28T14:00:56Z" level=error msg="cpu collector failed after 0.000981s: open /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq: no such file or directory" source="collector.go:142"

Thanks 👍

Edit:

On the other hand, this wouldn't stop the logging since I don't have a cpufreq anyways.

$ ls -al /sys/devices/system/cpu/cpu0/cpufre*
ls: cannot access '/sys/devices/system/cpu/cpu0/cpufre*': No such file or directory

[lukasmalkmus]

Technically it can be added. But currently I don't have the time to implement this myself.

I'll still accept contributions, tho.