Documentation needs to be updated / created following removal of /mautic/callback

Problem/Motivation

The project page says:

Note: redirect url should be yourdrupalsitename.com/mautic/callback

But that route in the module was removed in this commit prior to the 1.0.0 release:

commit a80eeee42eb715b373d31d60df42127c03f51d80
Author: Nick Vanpraet <nick.vanpraet@dropsolid.com>
Date:   Thu Apr 7 17:40:09 2022 +0200

    Switch to Client Credentials grant (requires patched library)

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes