Fix outdated zenohd.service and config files

[doganulus]

Describe the bug

The systemd unit file and the config file in the zenohd directory are probably outdated. These files are still installed from the Debian repos in version 1.3.3. Starting the service gives the following unknown field error when reading the config file as follows:

zenohd[66]: called `Result::unwrap()` on an `Err` value: JSON error: Message { msg: "unknown field `plugins_search_dirs`, expected one of `id`, `metadata`, `mode`, `connect`, `listen`, `open`, `scouting`, `timestamping`, `queries_default_timeout`, `routing`, `aggregation`, `qos`, `transport`, `adminspace`, `namespace`, `downsampling`, `access_control`, `low_pass_filter`, `plugins_loading`, `plugins`", location: Some(Location { line: 62, column: 3 }) } at commons/zenoh-config/src/lib.rs:979.

To reproduce

1. Install Zenoh from Debian repos on a fresh machine
2. Enable and start zenohd.service

System info

• Zenoh version 1.3.3