throw error when rule with the same name is found multiple times

[pkhabazi]

Summary of the Pull Request

This pr adds an extra validation step to the import-azsentinelalertrule function to throw an error when the is an alert rule with the same name found multiple tipes.

References

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PR Checklist

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• Closes #xxx
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx
• I have made only one major change in my proposed changes.
• I have commented my proposed changes within the code.
• I have tested my proposed changes, and have included unit tests where possible.
• It is compatible with the MIT License
• I have squashed any insignificant commits. (git rebase)

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Validation Steps Performed

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How does this PR accomplish the above

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