Add Notification asset model and related enums

[AngadSethi]

✨ Description

This PR introduces the Notification asset model and its associated enums. These additions lay the groundwork for handling notifications within the system.

Jira link: [Insert link here]

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🧩 Type of change

Select all that apply:

• 🚀 New feature (non-breaking change that adds functionality)
• 🐛 Bug fix (non-breaking change that fixes an issue) — please include tests! Refer testing-toolkit 🧪
• 🔄 Refactor (code change that neither fixes a bug nor adds a feature)
• 🧹 Maintenance (chores, cleanup, minor improvements)
• 💥 Breaking change (fix or feature that may break existing functionality)
• 📦 Dependency upgrade/downgrade
• 📚 Documentation updates

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✅ How has this been tested? (e.g. screenshots, logs, workflow links)

Describe how the change was tested. Include:

• Steps to reproduce
• Any relevant screenshots, logs, or links to successful workflow runs
• Details on environment/setup if applicable

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📋 Checklist

• My code follows the project’s style guidelines
• I’ve performed a self-review of my code
• I’ve added comments in tricky or complex areas
• I’ve updated the documentation as needed
• There are no new warnings from my changes
• I’ve added tests to cover my changes
• All new and existing tests pass locally