An update to the devnet to introduce a local heimdall to facilitate
multiple validators without the need for an external process, and hence
validator registration/staking etc.
In this initial release only span generation is supported.
It has the following changes:
* Introduction of a local grpc heimdall interface
* Allocation of accounts via a devnet account generator ()
* Introduction on 'Services' for the network config
"--chain bor-devnet --bor.localheimdall" will run a 2 validator network
with a local service
"--chain bor-devnet --bor.withoutheimdall" will sun a single validator
with no heimdall service as before
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Co-authored-by: Alex Sharp <alexsharp@Alexs-MacBook-Pro-2.local>
