Add Opossum Cow

[oohwooh]

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[github-actions]

🧪 PR Validation Results for #4

✅ Check PR is going to correct repo passed!
✅ Check image path passed!
✅ Check image file exists passed!
✅ Check image file size passed!
❌ Image file name in cows/opossum.json should be based on the cow's name. Expected: images/cowpossum.png or .jpg or .jpeg
❌ File cows/opossum.json is not properly indented.
✅ Check line endings passed!

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❌ 5/7 passed. Please fix the issues above and update your PR.

[github-actions]

🧪 PR Validation Results for #4

✅ Check PR is going to correct repo passed!
✅ Check image path passed!
✅ Check image file exists passed!
✅ Check image file size passed!
✅ Check file naming convention passed!
✅ Check proper indentation passed!
✅ Check line endings passed!

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✅ All tests passed! Nice work on your PR! 🎉