Update knowledge base with current API libraries for PHP

Hey there, I needed to use API for one of my projects and I was looking for a PHP library. Existing libraries were missing features and not supported so I wrote my own with all the possible features, including the latest custom sounds feature. It is very comprehensive library, if you guys are interested to list it in your knowledge base then please feel free. It has been installed over 11k times, has few stars and one dependent, and has been used for some time already. The library can be located here: https://github.com/slunak/pushover-php

In regards to other libraries listed in the knowledge base, here are my reasons why I did not choose to use them but instead developed my own:

cschalenborgh/php-pushover - this is very basic but working library, good for simple notifications but lacking a lot of features, for example image attachments. It works only with Message, Validation and Receipts API. Last commit that adds functionality was done in 2017, 5 years ago.

sqmk/Pushy - Last commit that adds functionality was done 6 years ago. Pull request not actioned since 2017. Seems abandoned. Works only with Message API.

LeonardoTeixeira/Pushover - well written code, simple library that works only with Message and Receipts APIs. Lacking features. Pull request to add Glances support is not accepted since 2019. Seems abandoned.

The rest of the libraries listed are related to Laravel framework so I did not review them as I am using Symfony framework. By the way, I am planning to write Symfony bundle with Pushover support using my library.

Let me know if you have any questions or comments, I will be happy share my thoughts.