Update postboard to use Lisk SDK 6.0

[reyraa]

In order to demonstrate the use of Lisk SDK 6.0, and benefit from this project in the development of WalletConnect protocol in Lisk Desktop and Mobile, we should update the Postboard project to use Lisk SDK 6.0.

[reyraa]

I faced an issue trying to imitate a project with Lisk SDK v6.0.0-alpha.0:

 Generating genesis block and config.
    TypeError: The "list[1]" argument must be an instance of Buffer or Uint8Array. Received an instance of Object
    Code: ERR_INVALID_ARG_TYPE
/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/yeoman-generator/node_modules/execa/lib/error.js:59
		error = new Error(message);
		        ^

Error: Command failed with exit code 1: /Users/reyraa/Projects/lisk/lisk-sdk-examples/tutorials/postboard/bin/run genesis-block:create --output config/default --validators-passphrase-encryption-iterations 1 --validators-hash-onion-count 10000 --validators-hash-onion-distance 1000
    at makeError (/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/yeoman-generator/node_modules/execa/lib/error.js:59:11)
    at Function.module.exports.sync (/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/yeoman-generator/node_modules/execa/index.js:188:17)
    at InitGenerator.spawnCommand.spawnCommandSync (/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/yeoman-generator/lib/actions/spawn-command.js:35:16)
    at InitGenerator.end (/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/dist/bootstrapping/templates/lisk-template-ts/generators/init_generator.js:54:14)
    at Object.<anonymous> (/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/yeoman-generator/lib/index.js:1009:25)
    at /Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/run-async/index.js:49:25
    at new Promise (<anonymous>)
    at /Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/run-async/index.js:26:19
    at runLoop.add.once.once (/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/yeoman-generator/lib/index.js:1010:11)
    at Immediate.<anonymous> (/Users/reyraa/.nvm/versions/node/v16.14.2/lib/node_modules/lisk-commander/node_modules/grouped-queue/lib/subqueue.js:48:34) {
  shortMessage: 'Command failed with exit code 1: /Users/reyraa/Projects/lisk/lisk-sdk-examples/tutorials/postboard/bin/run genesis-block:create --output config/default --validators-passphrase-encryption-iterations 1 --validators-hash-onion-count 10000 --validators-hash-onion-distance 1000',
  command: '/Users/reyraa/Projects/lisk/lisk-sdk-examples/tutorials/postboard/bin/run genesis-block:create --output config/default --validators-passphrase-encryption-iterations 1 --validators-hash-onion-count 10000 --validators-hash-onion-distance 1000',
  exitCode: 1,
  signal: undefined,
  signalDescription: undefined,
  stdout: undefined,
  stderr: undefined,
  failed: true,
  timedOut: false,
  isCanceled: false,
  killed: false
}

The issue is to be reported in the SDK repo.