Include pstore contents in show techsupport tarball

[saiarcot895]

Kernel panics can be written to pstore, which is a persistent file storage specifically for the kernel. On UEFI-based systems, this pstore is backed by UEFI, and the files written to pstore will be stored as EFI variables. On the next bootup, the systemd-pstore service will collect the files in pstore and copy them to /var/lib/systemd/pstore. This allows us to have the full dmesg logs including the kernel panic logs when a kernel panic does happen, without needing to be attached to the console of the device.

Currently, show techsupport doesn't include /var/lib/systemd/pstore in the files collected. This directory should be added so that kernel panic logs are included.