adding link to webhook portal

[nicolasburtey]

the query below will give a link to open the webhook portal, which can be very useful to debug the issues related to webhook.

we should add on the following page https://dashboard.blink.sv/callback a button that open this link so dev can more easily debug the issue they may have with callbacks

query Query {
  me {
    defaultAccount {
      callbackPortalUrl
    }
  }
}