Add example notebook: causal discovery with a foundation model + GCM root cause analysis

[bloebp]

Adds a new GCM example notebook showing that a plain CSV of observational data is sufficient for a full causal analysis: the causal graph is inferred with FoundCause, a pretrained foundation model for causal discovery (see Paper), and DoWhy's GCM module runs the analyses on the discovered graph.

The scenario is a simulated bottling line (ground truth via DoWhy's random SCM generator, including a hidden confounder), covering graph discovery, falsification with falsify_graph, root cause analysis of a defect spike and distribution-change attribution of a throughput drop.

[Copilot]

Pull request overview

Adds a new advanced documentation example notebook that demonstrates end-to-end causal discovery (via FoundCause) followed by DoWhy GCM analyses (graph falsification, anomaly attribution/root-cause analysis, and distribution-change attribution), and exposes it in the example notebook index.

Changes:

• Adds a new GCM example notebook: causal discovery from observational CSV data using FoundCause, then GCM-based analyses on the discovered graph.
• Updates the example notebook index to feature and include the new notebook in the Real world-inspired examples section.
• Ignores the local FoundCause model cache directory created when running the notebook.

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated 3 comments.

File	Description
docs/source/example_notebooks/nb_index.rst	Adds the new notebook to the grid cards and toctree so it appears in the rendered docs.
docs/source/example_notebooks/gcm_causal_discovery_foundcause.ipynb	New advanced notebook demonstrating causal discovery + GCM analyses on a simulated bottling-line scenario.
.gitignore	Ignores the notebook-created foundcause_model/ cache directory under docs/source/example_notebooks/.

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