Adds the following mandatory functions to setup.php to ensure the plugin
can be correctly registered and identified by GLPI:
- `plugin_version()`: Parses plugin.xml to provide metadata such as name,
version, author, and compatibility to GLPI.
- `plugin_init_options()`: Returns essential plugin identifiers like
its key and display name.
- Stub functions `plugin_check_prerequisites()`, `plugin_check_config()`,
and `plugin_display_config()`: Added to prevent potential errors and
serve as placeholders for future functionality.
These changes address the issue of the plugin not appearing in the GLPI
plugin installation interface.
