Migrate Codeigniter from 2.2 to 3.1.1

[pH-7]

Need to migrate Codeigniter from the current pH2Date Codeigniter version (which is 2.2.2) to the latest version
https://codeigniter.com/userguide3/installation/upgrade_300.html#upgrading-from-2-2-x-to-3-0-x

P.S. Codeigniter v4 is still under development stage.