Edited Domain Details Severity Level Formatting (CRASM-1055)

[hawkishpolicy]

• Brought the formatting of irregular severity levels displayed inside of Domain Details into line with the remainder of the app.

🗣 Description

• Forced title case on all severity levels.
• Null, N/A, undefined, and empty strings are now displayed as "N/A".
• Low, Medium, High, and Critical severity levels remain the same.
• All other values are now displayed as "Other".
• Brought in the corresponding severity level color values as well.

💭 Motivation and context

• Ensures the formatting of irregular severity levels remains constant across the app.
• Closes CRASM-1055

🧪 Testing

• tested locally.

📷 Screenshots (if appropriate)

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All new and existing tests pass.

✅ Pre-merge checklist

• Revert dependencies to default branches.
• Finalize version.

✅ Post-merge checklist

• Create a release.