feat(commands): add user context to remove_staff command

[Akinator31]

This pull request updates the remove_staff command to support both slash and user context menu invocations, improving its flexibility and error handling. The most important changes are:

Command registration and invocation

• Added support for registering remove_staff as a user context menu command by including a new CreateCommand with CommandType::User in the command registration.
• Updated imports to include CommandType for the new command registration.

Argument handling and error reporting

• Enhanced argument resolution logic to handle user context menu invocations by extracting the target user ID from command.data.target_id if arguments are missing, and improved error reporting for invalid or missing arguments.