Misc fixes in the GEM address tables

This MR aims at "fixing" the GEM address tables to comply with the XSD schema used to validate the XML files in the online software (see https://gitlab.cern.ch/cmsgemonline/gem-daq/cmsgemos/-/snippets/1977).

I'd also like to include the GEM_AMC -> GEM node renaming (needed for the production online software) in this MR. Are there any outstanding comments on !63 (merged)?