Adding the notebook for dynamic_embedding demo

[thushv89]

Description

This adds a notebook to demonstrate the usage of the dynamic_embedding module in the tensorflow_recommender_addons library.

Fixes # (issue)

Type of change

• Bug fix
• New Tutorial
• Updated or additional documentation
• Additional Testing
• New Feature

Checklist:

• I've properly formatted my code according to the guidelines
  • By running yapf
  • By running clang-format
• This PR addresses an already submitted issue for TensorFlow Recommenders-Addons
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

How Has This Been Tested?

N/A

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[rhdong]

Hi @thushv89, thank you for your excellent job. To avoid you missing my comments in the ReviewNB, just paste them here. Hope these comments can be helpful:

• The de.keras.layers.BasicEmbedding could be changed to de.keras.layers.Embedding, for we have v0.6.0 release to support them.
• It looks like the embedding size fluctuates too much, which may hurt the AUC of DE restrict. So setting the restrict configuration num_reserved from 0.8 to 0.95 would be better, and re-run testing is needed. -- This change may help get a higher AUC on restrict mode. (Please confirm the TFRA version is 0.6.0 when running the test.)
  Thank you so much!

[rhdong]

LGTM