Cardano Updates

— Add derived Show instance to ExecutionError
— Add reconfiguration endpoints
— Add tracing of timeseries API calls
— Add a bundle of tracers and thread it through
— Add a timeseries pruner thread

Allow testing block production with kes-agent via cardano-testnet
--use-kes-agent

John Lotoski found that it doesn't appear under any condition
(GenesisMode, PraosMode).  Now connection manager & peer selection
exposes a more detailed metrics including
`cardano_node_metrics_peerSelection_ActivePeers_int`