Prepare v5 release

[Simply007]

Motivation

Prepare version targetting PHP 8.

Related to #111

Checklist

• [ ] Code follows coding conventions held in this repo
• [ ] Automated tests have been added
• [ ] Tests are passing
• [ ] Docs have been updated (if applicable)
• [ ] Temporary settings (e.g. variables used during development and testing) have been reverted to defaults

How to test

If manual testing is required, what are the steps?

[codecov[bot]]

Codecov Report

Merging #114 (65af862) into master (3635bbf) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #114   +/-   ##
=========================================
  Coverage     98.12%   98.12%           
  Complexity      200      200           
=========================================
  Files            23       23           
  Lines           588      588           
=========================================
  Hits            577      577           
  Misses           11       11           

Impacted Files	Coverage Δ
src/Kentico/Kontent/Delivery/DeliveryClient.php	94.35% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 3635bbf...65af862. Read the comment docs.