Add a table page object function to get an icon's severity

[m-akinc]

Pull Request

🤨 Rationale

I'd like to be able to verify that icon severities are being set correctly in the Assets table.

👩‍💻 Implementation

Added a new page object function that gets the icon severity for a particular cell. It is very similar to the existing function for getting a cell's icon/spinner tag name.

🧪 Testing

N/A

✅ Checklist

• [x] I have updated the project documentation to reflect my changes or determined no changes are needed.