small improvements for parachains consensus (#2040)

* introduce a waiting period before selecting candidates and bitfields

* add network_bridge=debug tracing for rep

* change to 2.5s timeout in proposer

* pass timeout to proposer

* move timeout back to provisioner

* grumbles

* Update node/core/provisioner/src/lib.rs

* Fix nitpicks

* Fix bug

Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>