Update docs for new default-non-nullable default value in 7.x

[fitztrev]

Changes

Document new default as mentioned in the migration guide

How to Review

Verify against actual default value

Checklist

• Unit tests updated
• docs/ updated (if necessary)
• pnpm run update:examples run (only applicable for openapi-typescript)

[changeset-bot]

⚠️ No Changeset found

Latest commit: 93a57b2

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[drwpow-figma]

Thank you!