Safe validator initial start

[kyle-u410]

🚀 Feature

Less down time when starting a validator.

Motivation

For network launch in testnet, starting too many validators at the same time has caused network halts. These halts are avoidable if the validator is synced when the bond_validator call is made.

Implementation options

1. Running a node with start --validator in the case bond has not been called will run the node as client watching for bond_validator. As soon as that transaction is seen the node will shift to validator mode.
2. Allow bond_public transaction to be sent from validator when it catches up to head. This is effectively a script that runs the validator as a client and then when the client is close to tip issues the bond_validator

[Damon Sicore]

In our testing, we start validators all at once all the time and we don't see network halts. What are the details of these halts?