discover Slash Commands
Discover the BaseSlashCommand inside the package.
See also
Parameters
package Name
The package to lookup.
Throws
When you try to register more than 1 command with the same name, a command that contains a default handler with sub-commands handlers, a command contains more than 1 handler for the same command path (command/group/subcommand) or a command does not contain handlers.
When cannot initialize a command class with no empty constructor.