Adding link parameters to a relation

[tothewine]

I see there are some relation that have relation parameters (columns in the many many table). Where can I define them in metadata?
I am trying to add support for a custom entity in TargetList (on a 5.x version of espo) and I need to add the opted_out column.

[tothewine]

I solved by having a better look at documentation and existing relations of TargetList in entityDefs/TargetList.json