[New Tutorial] Using Keras 3 with pennylane (including full multi-backend support)

[vinayak19th]

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Title:
Keras 3 Training

Summary:
A demo showing how to integrate a pennylane circuit into keras 3 and train it using both pytorch and tensorflow

Relevant references:
None

Possible Drawbacks:
None

Related GitHub Issues:
None

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If you are writing a demonstration, please answer these questions to facilitate the marketing process.

• GOALS — Why are we working on this now?
  I implemented this support for a paper I was working on, and thought it would be useful as a general tutorial for everyone.

• AUDIENCE — Who is this for?
  For people who want to train QML models but have a Keras-based workflow for their ML stack. Also great for those who want to define a QML layer that can be integrated and trained with multiple ML backends without code changes.

• KEYWORDS — What words should be included in the marketing post?
  Quantum Machine Learning, Keras, Tensorflow, PyTorch, Jax, How-To, Tutorial

• Which of the following types of documentation is most similar to your file?
  (more details here)

• Tutorial
• Demo
• How-to

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[CatalinaAlbornoz]

Hi @vinayak19th,

Thank you for making this demo. I've responded in the Forum thread that you opened (#9060). We can keep the conversation there, or in the issue for the community demo if you decide to open one. Let us know if you have any questions.

For now I will close this PR since we will be moving to a community demo, which doesn't require a PR.