Implement Group Managed Service Account (gMSA) support

[henryttran]

This Pull Request introduces support for Group Managed Service Accounts (gMSA).

To enable Group Managed Service Accounts support, as per the winsw XML configuration file guidelines, the element must be excluded from the configuration.

https://github.com/winsw/winsw/blob/v3/docs/xml-config-file.md#service-account

Changes:

• Modified lib/winsw.js to conditionally add the password to the service account configuration based on svc.logOnAs.gmsa property.
• Added gmsa property to logOnAs object in lib/daemon.js to enable gMSA support.
• README.md updated with instructions for gMSA usage.

// Example usage

app.js 

var Service = require('node-windows').Service;
var svc = new Service({
  name:'Hello World',
  script: require('path').join(__dirname,'helloworld.js'),
  allowServiceLogon: true 
});
svc.logOnAs.domain = 'mydomain.local';
svc.logOnAs.account = 'username_$';
svc.logOnAs.gmsa = true;
...

[henryttran]

@coreybutler would you consider merging this? 😄

[coreybutler]

When I get a chance to review it/test it, yes. I'm pretty backlogged right now though.