Get rid of global configs

[DDtKey]

I think it's necessary to drop global configs and move them to structure-based ones.

Motivation: there are cases when an application should use different clients (I mean several fred-clients to different clusters/nodes), and they might have different configs (e.g default_connection_timeout_ms)

[aembke]

Most of these were removed in 7.x (https://crates.io/crates/fred/7.0.0-rc.1). I kept a few around that would be especially invasive or annoying to remove, but the important ones were moved to config structs.