IBX-4929: PHP API reference (#1904)

* Add a script to generate a PHP API reference
* Generate PHP API reference's HTML
* Add PHP API reference to the API chapter
* Links to PHP API reference

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Co-authored-by: Adrien Dupuis <[email protected]>
Co-authored-by: Michał Grabowski <[email protected]>
Co-authored-by: Tomasz Dąbrowski <[email protected]>
Co-authored-by: julitafalcondusza <[email protected]>