DOC - replacing gpt4 with gpt4o in example notebooks

[jsong468]

Description

Replacing gpt4 with gpt4o as default in most of the docs and renamed AzureOpenAIChatTarget --> AzureOpenAITextChatTarget. I kept the use of the AzureOpenAITextChatTarget in some of the demos so users can see how it's used, including the first part of the how_to_guide, many_shot_jailbreak, tree_of_attacks_with_pruning, and 3_custom_targets. In the targets folder, gpt4-o is now a core page while gpt-v and text only gpt are moved to supplementary pages. In the multi-modal targets demo, gpt-v is replaced by gpt4-o demo with text and image as input. Targets in the converters, scoring, memory pages use gpt4-o now. Tests remain using text-only gpt, and I changed the naming to AzureOpenAITextChatTarget.

Also added Crucible API key to env_example.

Tests and Documentation

I ran the notebooks without error and used jupyter nbconvert --to script command to convert from notebook to python script. All tests compiled and ran successfully.

[nina-msft]

Great job! A few minor comments but otherwise looks great :-) Let me know if you have any questions.