By term upcoming feature, I mean, we need this section in Turris OS 5.x,
but there is already present, but it is missing in Turris OS 3.x.
It results if you are  using Storage plugin then you can redirect the
syslog to /srv, but if there is missing source net, syslog-ng does not
start.

This should cover migration issue, however, syslog-ng.conf is conffile
which things complicated.