Consider adding railroad diagrams for the URL syntax

It may be helpful to have diagrams for the URL conventions, similar to https://www.odata.org/documentation/odata-version-2-0/uri-conventions/

Here's a nice diagram generator for EBNF: https://www.bottlecaps.de/rr/ui

Explore whether/how this can be used to visualize parts of our URL ABNF.

This looks quite nice (after a little cleanup) for the reduced OData URL syntax supported by SAP Graph