Add a caution note for embedding_lookup for CPU vs GPU behaviour
The API `embedding_lookup` have different behaviour on CPU vs GPU when there is out of range id passed to the argument `ids`.

On CPU it will raise error but on GPU it will output `0` to corresponding value. This is due to the reason that this API calls `tf.gather` internally where this constraint is mentioned.

I am proposing to add a caution note on this behaviour as requested by the author in #62628 .