CSJ dynamo policy selection/tuning

Based on input-output-hk/ouroboros-consensus#557, we should decide on the following properties of the jumping policy:

- Whether a static policy suffices our performance needs.
- How often to jump, balancing competing factors:
- high enough frequency to robustly avoid stalling the BlockFetch pipeline
- low enough frequency to effectively minimize load on the ledger peers (ie. the SPO relays acquired per se, not via peer sharing)

- How often to switch the dynamo (not ever switching it (other than in the case of disconnections) might be sufficient for the MVP; we can later tweak this using information from peer sharing).