build_examples.py need to support mdns option

[mikaelhm]

Problem

scripts/build/build_examples.py does not have an option to specify which mDNS option the example app should be build with. Currently builds default to use minmdns.

For certification we need to build apps with platform option to use avahi on the linux platform.
https://github.com/CHIP-Specifications/chip-certification-tool/issues/507

[davidgoogle]

I took a brief look, it seems like HostBuilder in host.py has a use_platform_mdns option, it just needs to be exposed as a Variant in targets.py.

[bzbarsky-apple]

@andy31415

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[bzbarsky-apple]

Fixed in #23856