Merge branch 'cs/#6921-remove-unused-variable-assignments'

Close #6921
allow to set DateTimeObject to the expires SetCookie expire ref #6673
added docblock comment
added missing docblock
removed slash for datetime docs
#6673 - importing used `DateTime` class
#6923 #6673 - minor docblock CS fixes
#6923 #6673 - adding missing `@group` annotations for newly introduced tests
Merge branch 'feature/#6923-allow-datetime-cookie-expires' into develop

Close #6923
Forward port #6923