allow passing filters to `.latest()` function

[digizeph]

Currently, if users want to get the latest data file for certain collector or data type, they need to call .latest() and filter the data with custom .filter function.

We should allow users to use the same filtering mechanism to filter .latest() results. The following example should work:

let latest_rcc00_rib = bgpkit_broker::BgpkitBroker::new().collector_id("rrc00").data_type("rib").latest();