Add dataset validation for sync push command

[DechengMa]

Adding validation and error handling logic for sync push command

📝 Summary of Changes

Changes proposed in this pull request:

• Add duplicateTesters error for handling duplicate testers with the same email addresses.
• Add noValidApp error when the user hasn't run sync pull before sync push

🧐🗒 Reviewer Notes

💁 Example

swift run asc testflight sync push

🔨 How To Test

swift run asc testflight sync push