Initialize Guard objects for unified management

[sgalcheung]

Currently, we need to create a guard on each page.

<script>
    const guard = new GuardFactory.Guard({
      appId: 'AUTHING_APP_ID'
    })

    guard.start('#authing-guard-container').then(userInfo => {
      console.log('userInfo in start: ', userInfo)
    })
  </script>

We could initiate a guard client and mount it to the window object. Centrally manage Guard, no need to create one each time. We can refer to createClerkClient.

Then we could use it easily

const guard = window.Guard;
// and call API
guard.load()