feat: add online serving w/multiple entities notebook

[mrkumar9001]

REQUIRED: Add a summary of your PR here, typically including why the change is needed and what was changed. Include any design alternatives for discussion purposes.

add online serving w/multiple entities notebook - introduces StreamingFetchFeatureValues API

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.

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[sen-sam]

Added a few nits. Main (global) feedback:

• Avoid the use of the first person (I/we).
• Avoid directional text such as "below". Preferred: "following".
• Having a description before a code sample can help improve usability.

[sen-sam]

I wonder if it's okay for us to surface the "SFFV" in the docs. Has its use in public artifacts been approved by Alex/Raiyaan?

[mrkumar9001]

For now Raiyaan has okayed usage. Will follow up with Alex.

[sen-sam]

I'm unfamiliar with this annotation. How is this rendered?

[mrkumar9001]

ptal at review NB link or via files.

[sen-sam]

Is this a standard text or can we shorten it to, say, "Wait for the kernel to restart before continuing to the next step"?

Also, I feel we should render this as a "Caution:" such as what's illustrated here i.e. without the icons: https://developers.google.com/style/notices

However, please feel free to ignore these comments if this is a standard note that's been used elsewhere.

[mrkumar9001]

This is standard from the template - https://github.com/GoogleCloudPlatform/vertex-ai-samples/blob/main/notebooks/notebook_template.ipynb. @gericdong to comment if this should be changed to caution?

[sen-sam]

Just one nit. LGTM otherwise!

[sen-sam]

Is this a standard text or can we shorten it to, say, "Wait for the kernel to restart before continuing to the next step"?

Also, I feel we should render this as a "Caution:" such as what's illustrated here i.e. without the icons: https://developers.google.com/style/notices

However, please feel free to ignore these comments if this is a standard note that's been used elsewhere.