[lldpd] Add plugin for the LLDP daemon

[suraj-cmd]

lldpd is packaged for Fedora, RHEL via EPEL, Debian and Ubuntu, but sos has no
plugin for it. networking.py collects /var/lib/lldpad/, which belongs to
lldpad, a separate implementation; nothing in the tree covers lldpd itself.

Paths are taken from upstream. src/daemon/lldpd.c passes
SYSCONFDIR "/lldpd.conf" and SYSCONFDIR "/lldpd.d" on resume, and
src/daemon/lldpd.service.in sources both /etc/default/lldpd and
/etc/sysconfig/lldpd as optional environment files, so both are collected
rather than assuming which one a distribution ships.

The lldpcli subcommands are those registered in src/client/show.c.
show neighbors details is the useful one for support: it records which switch
and port each interface is attached to, which cannot otherwise be recovered
from an sosreport.

The daemon holds no credentials, so no forbidden paths are needed.

Worth noting networking.py already collects /var/lib/lldpad/ for the
separate lldpad implementation — this plugin does not overlap with it, but a
reviewer may prefer the two be reconciled.

---

Please place an 'X' inside each '[]' to confirm you adhere to our Contributor Guidelines

• Is the commit message split over multiple lines and hard-wrapped at 72 characters?
• Is the subject and message clear and concise?
• Does the subject start with [plugin_name] if submitting a plugin patch or a [section_name] if part of the core sosreport code?
• Does the commit contain a Signed-off-by: First Lastname email@example.com?
• Are any related Issues or existing PRs

[packit-as-a-service]

Congratulations! One of the builds has completed. 🍾

You can install the built RPMs by following these steps:

• sudo dnf install -y 'dnf*-command(copr)'
• dnf copr enable packit/sosreport-sos-4428
• And now you can install the packages.

Please note that the RPMs should be used only in a testing environment.