Update Blockchain Data guide for compact block filters

[jkczyz]

https://github.com/lightningdevkit/rust-lightning/pull/1706 added proper support for compact block filters to the lightning-block-sync crate. The guide "Blockchain Data" guide needs to be updated such that (1) the code examples use the updated interface and more importantly (2) it talks about how to implement BlockSource (part of lightning-block-sync) and chain::Filter in order to support compact block filters.