Reorganize repository structure into three main sections

[CFLJacquet]

• 1-tracing: Basic tracing examples and custom evaluations
• 2-online-evaluation: Online evaluation examples and Ragas integration
• 3-experiments: Experiments, eval integrations, notebooks, and scripts

[cdfox]

When I preview this README (https://github.com/DataDog/llm-observability/blob/07baa86d22d5ea19ece3f840ad23342de9aff0f8/1-tracing/README.md) the image links are broken. I think it needs to be ../images/llm-span.png

[CFLJacquet]

Fixed

[cdfox]

Suggested change

	git clone https://github.com/DataDog/llm-observability-cookbooks.git
	cd llm-observability-cookbooks
	git clone https://github.com/DataDog/llm-observability.git
	cd llm-observability

[cdfox]

Ok, I just started from scratch, starting from the README of this repo on your branch.

• we don't need .env file in each directory, dotenv will find .env in the parent directory so user can just create once at top level of the repo
• I think we should direct the user to start notebook from top level of repo, and then they can navigate into the subdirectories to run through the notebooks
• we shouldn't need the READMEs within each subdirectory. I think it should just be the one README at top level of repo. Each notebook should stand contain any explanation needed about setup or how files are laid out. Notebooks are already a nice visual medium, once you have jupyter running.