Add vertex_ai_feature_store_iam_policy notebook.

[ethan-gordon]

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Add vertex_ai_feature_store_iam_policy notebook. This provides a tutorial on how to configure IAM Policy for Feature Store online serving resources.

REQUIRED: Fill out the below checklists or remove if irrelevant

1. If you are opening a PR for Official Notebooks under the notebooks/official folder, follow this mandatory checklist:

• Use the notebook template as a starting point.
• Follow the style and grammar rules outlined in the above notebook template.
• Verify the notebook runs successfully in Colab since the automated tests cannot guarantee this even when it passes.
• Passes all the required automated checks. You can locally test for formatting and linting with these instructions.
• You have consulted with a tech writer to see if tech writer review is necessary. If so, the notebook has been reviewed by a tech writer, and they have approved it.
• This notebook has been added to the CODEOWNERS file under the Official Notebooks section, pointing to the author or the author's team.
• The Jupyter notebook cleans up any artifacts it has created (datasets, ML models, endpoints, etc) so as not to eat up unnecessary resources.

2. If you are opening a PR for Community Notebooks under the notebooks/community folder:

• This notebook has been added to the CODEOWNERS file under the Community Notebooks section, pointing to the author or the author's team.
• Passes all the required formatting and linting checks. You can locally test with these instructions.

3. If you are opening a PR for Community Content under the community-content folder:

• Make sure your main Content Directory Name is descriptive, informative, and includes some of the key products and attributes of your content, so that it is differentiable from other content
• The main content directory has been added to the CODEOWNERS file under the Community Content section, pointing to the author or the author's team.
• Passes all the required formatting and linting checks. You can locally test with these instructions.

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[gericdong]

/gcbrun

[gericdong]

@ethan-gordon: please follow the notebook template: https://github.com/GoogleCloudPlatform/vertex-ai-samples/blob/main/notebooks/notebook_template.ipynb