Add rails_error_dashboard to Exception Notification category

[AnjanJ]

Summary

Adds rails_error_dashboard to the Exception Notification category.

rails_error_dashboard is an actively maintained, self-hosted error tracking engine for Ruby on Rails. Key highlights:

• 1,900+ RSpec tests plus integration chaos tests across 4 real Rails apps
• CQRS architecture (Commands/Queries/Services) for clean separation of concerns
• 100+ configuration options for flexible setup
• Multi-channel notifications: Email, Slack, Microsoft Teams, Discord, PagerDuty, custom webhooks
• Rails Engine — runs inside the host app's process with zero external service dependencies
• Broad compatibility: Ruby 3.2+ (including 4.0), Rails 7.0–8.1
• Rich dashboard with error analytics, trend charts, resolution tracking, and cause chain visualization

RubyGems: https://rubygems.org/gems/rails_error_dashboard
GitHub: https://github.com/AnjanJ/rails_error_dashboard

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Checklist per PR template:

• Referenced by gem name (rails_error_dashboard), not GitHub repository — it is published as a Ruby gem
• Alphabetical order maintained in the projects list