Request: add after() step

[regexj]

Before step is described here: https://github.com/pulsardev/vue-tour/wiki/Features

Please add the same functionality but for an after() step function. A callback for that specific step.

There are some cases where I would like to make XHR requests or modify the page contents after a step has loaded, not before. My current workaround is so:

//in case we have an after at the start, make sure it's triggered
onStartCallback () {
  this.runAnAfter();
}

previousStepCallback () {
  --this.vueTour.currentPageStep;
  this.runAnAfter();
}

nextStepCallback () {
  ++this.vueTour.currentPageStep;
  this.runAnAfter();
}

runAnAfter () {
  const step = this.vueTour.currentPageStep;
  if( this.vueTour.steps[step].after ){
    // @ts-ignore
    this.vueTour.steps[step].after();
  }
}

Then I've expanded the steps object to include that function

{
  target: '.not-found-wrapper',
  content: this.$t('vueTour.welcome.page.home.step2') as string,
  params: {
    placement: VueTourPlacement.Top
  },
  before: () => new Promise((resolve) => {
    //some logic here
    resolve(true);
  }),
  after: () => new Promise((resolve) => {
    //some logic here - e.g. xhr request prepares content for the next step without delaying the experience of loading the current step
    resolve(true);
  })
},