Split account from auction settings

[bretg]

Is your feature request related to a problem? Please describe.

During initialization, the SDK asks for "account". This value is then copied to two places in the ORTB:

• app.publisher.id
• ext.prebid.storedrequest.id

This is sub-optimal because a single account ID might want to have multiple top-level storedrequests defining different timeouts, price granularities, etc.

Describe the solution you'd like

I would like an optional parameter for the SDK to separate out account from "auction settings".

e.g.

Prebid.init(context, accountID, adServer, host, [auctionSettingsId]);

If specified, the auctionSettingsId is used to set ext.prebid.storedrequest.id. If not specified, it's ok to default ext.prebid.storedrequest.id to the account ID.

Describe alternatives you've considered

When we have the new ORTB feature defined in #877, there will be a workaround where the app code can override ext.prebid.storedrequest.id. But that seems awkward.