[Groundedness] Add example for context grounding

[ahibrahimm]

Description

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Pull request overview

This pull request adds a new example to the groundedness_with_query.prompty template file to demonstrate an important concept about context grounding in RAG evaluation systems. The PR title indicates this is specifically adding "an example for context grounding."

Changes:

• Added a new example to the "Groundedness: 5" rating section that uses intentionally incorrect factual information (Cairo as Japan's capital) to illustrate that groundedness evaluation measures faithfulness to the provided context, not real-world factual accuracy.