multi: Add batched cfilter fetching messages

[matheusd]

Close #3206

This adds the getcfsv2/cfiltersv2 set of messages, intended to be used by SPV clients to fetch batches of version 2 committed filters during their initial sync process.

Summary of changes:

• Record how max (worst) cfilter sizes may be calculated for various scenarios for the current network parameters and future proof them by adding a test that breaks if any of the parameters change
• Add getcfsv2/cfiltersv2 wire message and add a new protocol version that supports them
• Add an internal blockchain function that fetches batches of cfilters
• Hook the peer and server packages to respond to the getcfsv2 message