cubicweb #2742453 [web] give access to the request body [validation pending]

some http requests have a body, cw should give views access to it.

prioritynormal
typeenhancement
appeared in<not specified>
done in3.17.0
load0.500
load left0.000
closed by#8879:e19f4bba89cd
patchAdd CubicWebRequestBase.content [applied]