Improved email whitelisting for self-hosters

[Kritik-J]

Closes #833

✅ Checklist

• [x] I have followed every step in the contributing guide
• [x] The PR title follows the convention.
• [x] I ran and tested the code works

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Changelog

• Reject GitHub OAuth users not on the email whitelist
• Implement email whitelist check before sending magic link emails

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Video

https://github.com/triggerdotdev/trigger.dev/assets/82360525/7d760b4c-2be2-4de6-b610-2a90648884a2

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Latest commit: 182adc5b6558b4cee93785d90253f5c83a5c95ad

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