The 'classname' attribute was causing a warning during plugin installation
as it's not a recognized option in the Plugin::registerClass method for
this type of class.
This commit removes the unnecessary attribute, relying on the standard
behavior where the class name is inferred from the first argument.
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.
