feature: support custom balance allocation to nodes

[abhinavmsra]

Current State

Node balance value assigned in genesis.json is hardcoded to always be 1000000000000000000000000000

"alloc": {
    "0x11d3559cdfbdaf31cfce809567222e0aa686d6e1": {
      "balance": "1000000000000000000000000000"
    },
    "0x1b3c32173fa916d68460ca7fc902c279198db10f": {
      "balance": "1000000000000000000000000000"
    },
    "0xf0860e25455fcecc54b9a9d8f7a113c3fcbc26f8": {
      "balance": "1000000000000000000000000000"
    },
    "0x677a650e0e430028e028af1338a7e99c1cf796cf": {
      "balance": "1000000000000000000000000000"
    },
    "0xf7a2c90071bde5b192f72e46eb8596c01d47884e": {
      "balance": "1000000000000000000000000000"
    },
    "0x29eabbd71b43178e0eb3e1c431636b5ea0298376": {
      "balance": "1000000000000000000000000000"
    },
    "0x1b8f4cc25e76b0bbf84437d489a0a43382a7f286": {
      "balance": "1000000000000000000000000000"
    }
  }

Change

To allow for more control over supply & balance split between nodes & prefundedAccounts, this PR

• Introduces a new cli option & new question

  
  --genesisNodeAllocation

Balance allocated to each nodes: (default 1000000000000000000000000000)

- its value default to `1000000000000000000000000000` for backward compatibility

[chris-haven]

This PR has been open for a while. Is there a chance for a review?