Add a hook for plugins to add HTML code on pages
Modifying `Html::footer()` would allow plugins to add code on/as footer.
More method are impacted because some are dedicated to the help pages, modal/pop-up, etc.
I suggest adding hooks (say `$PLUGIN_HOOKS['add_code_in_header']` and `$PLUGIN_HOOKS['add_code_in_footer']`) for the plugin to allow more customization of GLPI general interface.
In my case, I am building a plugin to add snippets of plain HTML codes (disclaimers, notes, analytic trackers, etc.) on any pages.
Customer support service by UserEcho
This has already been implemented in the upcoming GLPi 9.1.2