Allow to update config. <site.json> later anytime

[heimdallrj]

Command:

wp config update <config_key> <config_value>

• Update site.json accordingly
• Do the changes on the code-base as necessary

Key fields allows to update

env.js

  allowUpdate: {
    config: [
      'mysqlDbHost',
      'mysqlDbPort',
      'mysqlDbUser',
      'mysqlDbPwd',
      'mysqlDbName',
      'mysqlDbTblPrefix'
    ]
  }