updater-ng: Update to version 70.1.0
Provides function get_turris_serial
returning serial number to be
used inside Lua. This will help us to implement staged updates. The rest
will be implemented in Lua, but we need to support it before we will
deploy the Lua code.
It is new feature, but would like to deploy building blocks through the minor versions to make it ready and enable it's use once we will do a big release.