feat: Pre-Fill input fields given url query parameter

[rgon]

This PR implements pre-filling form fields given url query parameters, as requested in #145

I have implemented this feature in the formReady method. For ease-of-use, it follows the same standard as cal.com:

You can add anywhere in the booking flow before the booking form page or in the booking form page itself. Simply add these in the URL and you're good to go!
https://cal.com/johndoe/book?email=johndoe%40example.com&phone=1234
Source: https://cal.com/docs/core-features/bookings/prefill-fields#pre-filling-all-fields

It also implements hiding the pre-filled inputs, so that in custom embed flows, we could just iframe the appointments app with the calendar component by setting hidePrefilledInputs=true

https://mycloud.tld/appointments/appointmentID?name=UserName&email=userEmail&hidePrefilledInputs=true

This PR also updates the documentation, referencing this change.

[SergeyMosin]

Thank you. This looks good. We also will need to add a setting for the users to enable/disable this feature. And maybe an option to display the Pre-Filled data in plain text in addition to hidePrefilledInputs

[rgon]

Thank you for this project!

I agree that disabling pre-filled values is a good idea. I have implemented this with the disablePrefilledInputs query param and updated this PR:

[rgon]

Regarding enabling it via the page settings, I have to dig deeper in the code to find out how to implement it. Will update the PR when I figure it out.

[SergeyMosin]

Regarding enabling it via the page settings, I have to dig deeper in the code to find out how to implement it. Will update the PR when I figure it out.

Don't worry about this, I'll add it after merging.