Upstream tutorials are missing the Vertex AI provider

[zimeg]

Summary

Great callout from @calvingiles with recent updates in #11:

I was reading the docs again and noticed that they replicate some of the instructions here - you might want to add some of the additions from the readme there too?

It is true that these docs and README don't match after the updates, though it'd be nice to keep these close in spirit IMO. Updates to the tutorial might add the Vertex AI provider and setup instruction 👀

We might also want to note some of this process in a MAINTAINERS_GUIDE since these updates aren't immediate when making changes to this sample IMO. I'm not sure if that page could be sourced from this sample to match updates to code and docs, but that might be more of a nice to have 🤔