Add Python notebook examples for the EOSC publish-tool

[Copilot]

Bootstraps the repo with a set of Jupyter notebooks covering the full EOSC publish-tool workflow, plus supporting docs and dependencies.

Added

• notebooks/01_getting_started.ipynb – credential setup via env vars (EOSC_API_TOKEN, EOSC_API_BASE_URL), connectivity check
• notebooks/02_data_access.ipynb – catalogue search, metadata retrieval, streaming file download into pandas
• notebooks/03_data_publishing.ipynb – end-to-end publish flow: prepare → SHA-256 checksum → build metadata → POST /datasets → upload file → POST /datasets/{id}/publish
• requirements.txt – requests, pandas, notebook, jupyterlab
• README.md – expanded with notebook table, install steps, env var config, and repo structure

Example workflow (notebook 3)

record = create_dataset(metadata)          # POST /datasets
upload_file(record["id"], csv_path)        # POST /datasets/{id}/files
publish_dataset(record["id"])              # POST /datasets/{id}/publish

Original prompt

create a repo for python notebook examples