Register ttyd service using mDNS

Bug: 373533555
Test: in the VM, `avahi-browse -art` gives
=    lo Ipv4 terminal
  Web Site         local
  hostname = [linux.local]
  address = [127.0.0.1]
  port = [7681]
  txt = []

and `avahi-resolve -n -4 linux.local` gives
linux.local  192.168.0.2

Change-Id: I0308c3d1b94272f66762000461576e61305c5565
diff --git a/build/debian/fai_config/files/etc/avahi/services/ttyd.service/AVF b/build/debian/fai_config/files/etc/avahi/services/ttyd.service/AVF
new file mode 100644
index 0000000..64f9d0a
--- /dev/null
+++ b/build/debian/fai_config/files/etc/avahi/services/ttyd.service/AVF
@@ -0,0 +1,13 @@
+<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
+<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
+
+<service-group>
+
+  <name>ttyd</name>
+
+  <service protocol="ipv4">
+    <type>_http._tcp</type>
+    <port>7681</port>
+  </service>
+
+</service-group>
diff --git a/build/debian/fai_config/package_config/AVF b/build/debian/fai_config/package_config/AVF
index a91c354..c779021 100644
--- a/build/debian/fai_config/package_config/AVF
+++ b/build/debian/fai_config/package_config/AVF
@@ -1,4 +1,7 @@
 PACKAGES install
 
+avahi-daemon
+avahi-utils
 bpfcc-tools
+libnss-mdns
 procps