Add minimal movielens KJT + EBC example

[vaishnavirao24]

Summary

This PR introduces a minimal example under torchrec/examples/ that demonstrates how to use KeyedJaggedTensor (KJT) in combination with EmbeddingBagCollection (EBC).

Details

• Sets up dummy user interaction data with a single sparse feature: "movie_id".
• Constructs a KeyedJaggedTensor using keys, values, and lengths.
• Passes the KJT through an EmbeddingBagCollection with an EmbeddingBagConfig.
• Prints the shape of the output embedding (expected: (5, 16)), where 5 is the batch size and 16 is the embedding dimension.

Motivation

This example serves as a clear, minimal reference for new users looking to understand how to integrate KJT with EBC effectively in TorchRec.

[TroyGarden]

suspecting ai-bot work.