Library initialization fails when environment variable `OPENAI_KEY` is missing

When using RobotframeworkAI library, the library cannot be instantiated when OPENAI_KEY is not an environment variable. That breaks already the autocompletion in IDEs with language server plugins.

This is the "problem" raised in VSCode (using Robotcode) when typing:

*** Settings ***
Library    RobotframeworkAI

Initializing library 'RobotFrameworkAI' with no arguments failed: KeyError: 'OPENAI_KEY'
Traceback (most recent call last):
  File "/home/noordsestern/git-repos/traveljunkies/.conda/lib/python3.11/site-packages/RobotFrameworkAI/__init__.py", line 24, in __init__
    libraries = [RealTestDataGenerator(), Chatbot(), Assistant()]

In general, library initialisation should not throw any exception. The initialisation should be lasy Like this, even libdoc cannot be generated when the environment variable is missing. Furthermore, API keys are usually injected by vaults or external mechanisms and are not present when writing test cases.

Start at RobotFrameworkAI/init.py, especially the initialization path shown at line 24, and reproduce library loading without OPENAI_KEY. Done means library initialization and libdoc generation no longer raise when the variable is absent, while AI-dependent use remains deferred until credentials are available.