Vendor the sunspec plugin into this repo so the Fronius work and the
upstream storage fixes can live here. Sources only: build artefacts and
generated plugininfo headers are excluded.
libnymea-sunspec is deliberately NOT vendored - the plugin must stay
rebasable on upstream nymea, so it links against libnymea-sunspec-dev.
sunspec.pri resolves it via pkg-config, with a NYMEA_SUNSPEC_PATH
override for a local sysroot, mirroring modbus.pri.
See sunspec/VENDORED.md.
