fix(api): unsubscribe all subscribed emails

[ShaunSHamilton]

Checklist:

• I have read and followed the contribution guidelines.
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• My pull request targets the main branch of freeCodeCamp.
• I have tested these changes either locally on my machine, or GitPod.

Related #40773 (Only to be closed, once new api is deployed)

Before	After
Unsubscribing accounts with the same email but different unsubscribeIds would result in emails still being sent	Unsubscribing accounts with the same email but different unsubscribeIds unsubscribes all accounts
All accounts with same unsubscribeId get unsubscribed	All accounts with same unsubscribeId get unsubscribed

These changes could be backported to the old/current api. However, I find it unscrupulous.

[ojeytonwilliams]

I like it, but why not both unsubscribeId and email? The chance of duplicate ids is low, but it should be quick to do both (assuming indexes are correct). Nevermind, I see it now!

[ojeytonwilliams]

LGTM 👍