Sync caching logic with Prebid Server Java

[mike-hoyt-ttd]

The current returnCreative/caching logic is confusing, and doesn't work well when there are bids with multiple different media types (video + banner). I've decided to sync the functionality up with PBS Java.

Changes

• Use separate flags for returnCreativeBids/returnCreativeVast instead of a single returnCreative
• Only strip adm if the bid was actually cached

Behavior Comparison

Cache Config	IsVideo	ADM (old behavior)	ADM (new behavior))
vastxml.returnCreative=false only	No	Stripped	Kept
vastxml.returnCreative=false only	Yes	Stripped	Stripped
bids.returnCreative=false only	No	Stripped	Stripped
bids.returnCreative=false only	Yes	Stripped	Stripped
bids.returnCreative=true, vast.returnCreative=false	No	Kept	Kept
bids.returnCreative=true, vast.returnCreative=false	Yes	Kept	Stripped
bids.returnCreative=false, vast.returnCreative=true	No	Kept	Stripped
bids.returnCreative=false, vast.returnCreative=true	Yes	Kept	Stripped
Cache config set, but no targeting enabled	No	Stripped	Kept
Cache config set, but no targeting enabled	Yes	Stripped	Kept

[JonKale]

Massively not a concern but I'm curious why this and not e.g.

type extCacheInstructions struct {
	cacheBids          bool
	cacheVAST          bool
	returnCreativeBids bool
	returnCreativeVast bool
}

or

type extCacheInstructions struct {
	cacheBids, cacheVAST bool
	returnCreativeBids, returnCreativeVast bool
}

(but note that this is not a blocker)