consolidation by moving balance upon exit

[fradamt]

First attempt at a simpler consolidation design, suggested by @mkalinin, where the Consolidation simply exits the validator and then moves the balance upon exit. No slashing across source and target because churn is applied to the exit, and the moving balance earns rewards throughout, by the source until the exit epoch and then by the target

[yokem55]

It seems to me that the way to make this work is to restrict exit_transfer exits to a 7002 based exit (a message from the withdrawal address on el), or a message signed by with a 0x00 credential on the beacon chain. The validator key would still be able to do traditional exit messages that simply withdraw to the 0x01 credential, but would not be able to do the transfer side of things.