How to use network follow to choose part of the network - and use it as selection for eg. INTERLIS export

[sjib]

Description: You can use the network follwoing tool (upstream / downstream) to select a part of the network and use it as selection input for reaches and wastewater structures for the INTERLIS export - this video shows how: https://user-images.githubusercontent.com/1265865/139002941-5822af4c-b2e8-440a-9064-afb9080cb977.mp4

Related issue:

• [ ] https://github.com/QGEP/docs/issues/165