Updating the setup Wizard

[BrunoPavlinic98]

The goal of this task is to improve the current (wp-admin/admin.php?page=wpo-wcpdf-setup) PDF Invoices onboarding process.

We want to update the styles and see if we can shorten the amount of steps, and highlight the features of our paid extensions with a link to the upgrade tab.

[BrunoPavlinic98]

@Terminator-Barbapapa Here are my initial comments on the PDF Invoices onboarding improvements.

First, I think that the current setup for "separate page onboarding" is great and I would not touch it. I agree that it looks a bit outdated, but it provides all the necessary information for someone to get started, and I would argue that in the onboarding process, simplicity must be the goal, not stunning design. Therefore, I would leave this as is.

Regarding the onboarding after the user sets up the separate page onboarding, we currently have one admin pointer. I was looking into something similar to intro.js (they have a live demo), but then I thought that we can achieve the similar behavior using admin pointers. Therefore, I have created a demo for this idea:
https://github.com/user-attachments/assets/d9b7c785-c59b-4ee1-a89c-aba4fe8eba3c

This is just a basic example, but we could try to do the following with it:

1. Expand the functionality so that the next button can also lead users to other pages or tabs.
2. Do a nicer styling in terms of highlighting the HTML elements that we want to highlight, with the instructions in the admin pointer.

The idea is to make admin pointers work as similar as intro.js, and to make a nice onboarding story for the users to follow.

What do you think?