Change RegisterHandler path for RelayHandler, Go ServeMux no longer considers * a wildcard

[theJC]

Change RegisterHandler path for RelayHandler, Go ServeMux does not (any longer) consider * a wildcard

golang/go#68856 (comment)

[lleadbet]

This is a fun one, since we initially built this using Go 1.22, which as the issue notes, was supported (even if undocumented), and the Docker image actually accounts for this. I was exploring the option of using a different approach to do the same thing (using a dummy path parameter) but hadn't gotten around to polishing just yet.

Doing root path alone probably makes sense, but would just need clarity in the README about the fact the config has to match exactly. I can work with you in the PR on that, however.