Dynamic autostake batchTxs

The autostake transaction batch size is configurable and the default size is adjusted for a few networks. This is ultimately down to the max_gas BlockParam which defaults to 100m but this is sometimes changed.

REStake should query the node for the max_gas param and dynamically adjust the TX size to fit. TBC what percentage of max_gas we want to use, but this can likely be made configurable.