avahi: Add HDC service file for DNS-SD/mDNS discovery

To discover the targets IP address and HDC service running on it we offer a avahi service file.

An example command on the host to discover it would be: avahi-browse _workstation._tcp --terminate -r

Signed-off-by: Stefan Schmidt stefan.schmidt@huawei.com

recipes-connectivity/avahi/avahi/hdc.service

+<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
+<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
+<service-group>
+<name replace-wildcards="yes">OpenHarmony Device Connector on %h</name>
+<service>
+<type>_workstation._tcp</type>
+<port>35000</port>
+</service>
+</service-group>