Move over from '_ret' in name of ESDL pipes to 'related' field to define related pipes for supply and return

[lfse-slafleur]

See also here for the related field in Pipe description:
https://energytransition.github.io/#router/doc-content/687474703a2f2f7777772e746e6f2e6e6c2f6573646c/Pipe.html

[lfse-slafleur]

Coordinated release.

• Frontends use both 'related' & _ret naming ahead of optimizer & simulator changes.
• Components: NWN-DTK frontend (easy to change), mapeditor (Ask Ewoud & Edwin on how difficult this is), optimizer, simulator, ESDL validator? (Ask Femke)

Sebastiaan will pull this.