Support cache ttl for audio and native

[bretg]

PBS supports different cache lengths for mediatypes banner and video. Should we consider splitting this out to support native and audio?

In considering this for issue https://github.com/prebid/prebid-server/issues/2975, I realized that our cache length ought to be capped by the bidder's ORTB exp parameter. Perhaps we're already doing this?

[bretg]

Discussed in backlog meeting:

• agreed that extending cache length controls to native and audio makes sense. Just mediatypes, though, and DOOH is not a mediatype.
• Agreed that cache length should be capped by any exp parameter. Go and Java teams to look into whether this is already the case.

[SyntaxNode]

PBS-Go already allows default cache values to be defined for all media types (banner, video, audio, native) and the exp field is already taken into consideration during cache length calculation.

[bretg]

Discussed in committee

• Agreed on account level config: cache-ttl.{banner,video,audio,native}
• Hardcoded defaults should be
  • banner: 300
  • video: 1500
  • native: 300
  • audio: 1500

PBS-Java uses different config for banner/video that will be deprecated.

[bretg]

Working with the Java team, this is the order of how the cache length is determined:

1. bid.exp
2. corresponding imp.exp
3. ext.prebid.cache.{bids/vastxml}.ttlseconds
4. account.auction.{banner/video}-cache-ttl - deprecated. To be removed in a future major release.
5. cache.{banner/video}-ttl-seconds - deprecated. To be removed in a future major release.

To these, PBS-Java will add the config that PBS-Go has at https://github.com/prebid/prebid-server/blob/a6dea2f26d0dcf9e20c30de8297dad8931a319ee/config/config.go#L870

6. cache.default_ttl_seconds.{banner,video,native,audio}