cubicweb #2154655 cw.web.http_cache.GMTOFFSET is erroneous [validation pending]

once a running server passed a DST transition. IMO we should rather generate usage of UTC time internally instead of such hasardous computation.

priorityimportant
typebug
done in3.21.0
load0.500
load left0.000
closed by#937deb71a681 [web] kill GMTOFFSET (closes #2154655)
patch[debian] Add a Breaks for cubicweb-folder which stills use GMTOFFSET [applied][web] kill GMTOFFSET (closes #2154655) [applied][web/request] don't play tricks with utc offset [applied]