config: Handle miscellaneous time zones also
config: Handle miscellaneous time zones also

- In appears that in Debian it is possible to set the timezones from one
  of the listed items in zonetab.info or addtitional timezones from the
  directory /usr/share/zoneinfo/Etc/.  Add these too.

- By default all FreedomBox images have Etc/UTC as time zone.  This is
  now properly listed.

harry-7/Plinth,freedomboxtwh/Plinth,vignanl/Plinth,kkampardi/Plinth,freedomboxtwh/Plinth,freedomboxtwh/Plinth,kkampardi/Plinth,harry-7/Plinth,kkampardi/Plinth,jvalleroy/plinth-debian,vignanl/Plinth,vignanl/Plinth,harry-7/Plinth,freedomboxtwh/Plinth,vignanl/Plinth,vignanl/Plinth,harry-7/Plinth,jvalleroy/plinth-debian,jvalleroy/plinth-debian,jvalleroy/plinth-debian,kkampardi/Plinth,jvalleroy/plinth-debian,kkampardi/Plinth,freedomboxtwh/Plinth,harry-7/Plinth