cubicweb #3161654 [cache] make dogpile.cache available for cubicweb and cubes [in-progress]

And use it first (at least as a POC) for entity attributes transforms (some of these, e.g. rest to html, can take long enough to render that it is worthwhile to cache them).

prioritynormal
typeenhancement
done in<not specified>
load1.000
load left1.000
closed by<not specified>
patch[cache] use dogpile.cache to provide a simple cache for entity attributes transforms (closes #3161654) [rejected]