Adding multiple unique keys

[runleonarun]

Closes #6343

What are you changing in this pull request and why?

Adds multiple unique keys as outline in this plan.

Checklist

• I have reviewed the Content style guide so my content adheres to these guidelines.
• The topic I'm writing about is for specific dbt version(s) and I have versioned it according to the version a whole page and/or version a block of content guidelines.
• I have added checklist item(s) to this list for anything anything that needs to happen before this PR is merged, such as "needs technical review" or "change base branch."
• The content in this PR requires a dbt release note, so I added one to the release notes page.

---

🚀 Deployment available! Here are the direct links to the updated files:

• https://docs-getdbt-com-git-mult-unique-keys-dbt-labs.vercel.app/docs/build/snapshots
• https://docs-getdbt-com-git-mult-unique-keys-dbt-labs.vercel.app/reference/resource-configs/unique_key

[vercel]

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Name	Status	Preview	Updated (UTC)
docs-getdbt-com	✅ Ready (Inspect)	Visit Preview	Nov 14, 2024 1:01am

[runleonarun]

Next steps

• Test the code example
• Get DX review

[runleonarun]

Hey @dbeatty10 This is ready for you to review! I tested the code snippet in the IDE and it worked (hopefully I did that right 😆 ):

[dbeatty10]

Looks good to me @runleonarun 👍

[mirnawong1]

lgmt @runleonarun with a small sugg