Merge branch 'hotfix/#6907-allow-0-valued-headers'

Close #6907
set the datetime format from ISO8601 to ATOM to display correct timezone definition
added group issue docblock
fixed the method name
#6935 #6358 - adding test `@group` annotation referencing PR number
Merge branch 'hotfix/#6935-#6358-wrong-zend-feed-atom-datetime-format' into develop

Close #6935
Close #6358
Forward port #6935
Forward port #6358