Add ISO 3166 Code to proceedings attendees page

`owner:rcross@amsl.com` `resolution_fixed` `type_defect`   |    by rcross@amsl.com

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97 doesn't have it
https://datatracker.ietf.org/meeting/97/proceedings/attendees/

96 does
https://www.ietf.org/proceedings/96/attendee.html

Modify
ietf/templates/meeting/preceedings/proceedings_attendees_table.html

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_Issue migrated from trac:2228 at 2022-03-04 05:46:44 +0000_