Hardcoded creation date-time replaced by attribute "docprodtime"

Requires changes to the github workflow as commented in the PR

cf-conventions.adoc

@@ -1,7 +1,7 @@
 include::version.adoc[]
 = NetCDF Climate and Forecast (CF) Metadata Conventions
 Brian{nbsp}Eaton; Jonathan{nbsp}Gregory; Bob{nbsp}Drach; Karl{nbsp}Taylor; Steve{nbsp}Hankin; Jon{nbsp}Blower; John{nbsp}Caron; Rich{nbsp}Signell; Phil{nbsp}Bentley; Greg{nbsp}Rappa; Heinke{nbsp}Höck; Alison{nbsp}Pamment; Martin{nbsp}Juckes; Martin{nbsp}Raspaud; Randy{nbsp}Horne; Timothy{nbsp}Whiteaker; David{nbsp}Blodgett; Charlie{nbsp}Zender; Daniel{nbsp}Lee; David{nbsp}Hassell; Alan{nbsp}D.{nbsp}Snow; Tobias{nbsp}Kölling; Dave{nbsp}Allured; Aleksandar{nbsp}Jelenak; Anders{nbsp}Meier{nbsp}Soerensen; Lucile{nbsp}Gaultier; Sylvain{nbsp}Herlédan; Fernando{nbsp}Manzano; Lars{nbsp}Bärring
-Version {current-version}, 31 August, 2022
+Version{nbsp}{current-version},{nbsp}{nbsp}{docprodtime}
 :doctype: book
 :pdf-folio-placement: physical
 :sectanchors:

history.adoc

@@ -7,6 +7,7 @@
 
 === Working version (most recent first)
 
+* {issues}457[Issue #457]: Creation date of the draft Conventions document 
 * {issues}458[Issue #458]: Fix broken link to Unidata documentation.
 * {issues}423[Issue #423]: Always use "strictly monotonic" when describing coordinate variables
 * {issues}420[Issue #420]: Add List of Figures