Portal Bridge Add census record offer result for multiple items

[KolbyML]

Currently we only supported updating our census from single offers.

We have 2 unique cases with offering multiple items

• if it is a series of ephemeral header's then they should be treated as 1 unit, I haven't thought of how it would make sense to handle this. Read the Ephemeral Headers by Offer for context https://github.com/ethereum/portal-network-specs/blob/master/history/history-network.md#ephemeral-header-by-offer
• MultiOffer's with random non-ephemeral context this case can be handled almost identically to Offer case