Install Avahi runtime libraries under Linux

[adamrehn]

In the Unreal Engine 5.7.0 release, the NDIMedia plugin has evidently introduced a dependency on the Avahi runtime libraries under Linux.

As can be seen in this commit that added support for Linux and macOS, the plugin now ships with a shared library named libndi.so.6 and dynamically loads it at runtime. Examining the dependencies of that library outside of a container shows the following:

$ ldd libndi.so.6 
	linux-vdso.so.1 (0x000078e0f3890000)
	libavahi-common.so.3 => /lib/x86_64-linux-gnu/libavahi-common.so.3 (0x000078e0f3864000)
	libavahi-client.so.3 => /lib/x86_64-linux-gnu/libavahi-client.so.3 (0x000078e0f3850000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x000078e0f384b000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x000078e0f3754000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x000078e0f374f000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x000078e0f1600000)
	/lib64/ld-linux-x86-64.so.2 (0x000078e0f3892000)
	libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x000078e0f36f7000)
	libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x000078e0f18c1000)
	libcap.so.2 => /lib/x86_64-linux-gnu/libcap.so.2 (0x000078e0f36e9000)

The files libavahi-client.so.3 and libavahi-common.so.3 are not currently included in our Linux images, which results in cooking failures when creating an Installed Build of the engine. Those libraries are provided by the libavahi-client3 and libavahi-common3 packages, respectively, although libavahi-client3 has a dependency on libavahi-common3 so simply installing libavahi-client3 is sufficient to pull in both libraries.