Update .env.example

[mylee04]

Add a new "Supabase" connection necessary keys

Description

Please provide a brief description of the changes introduced in this pull request.

Related Issues

Closes #<issue_number>

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation, if necessary.
• I have added tests that prove my fix is effective or my feature works.
• New and existing tests pass locally with my changes.

Screenshots (if applicable)

Additional Notes

[vercel]

@mylee04 is attempting to deploy a commit to the Vercel Team on Vercel.

A member of the Team first needs to authorize it.

[QuentinFrc]

As documented the default database is Neon.
You can use Supabase if you prefer (adding the corresponding env vars to .env.example), but note that it's not related to this repo.