docs: add missing notification channels and config events

[Copilot]

Update Notifications Guide

This PR updates the notifications guide to ensure all notification options are properly documented with accurate examples.

Changes Made

New Channel Documentation

Added documentation for 4 missing notification channels:

• Bark - iOS push notification service
• Google Chat - Google Chat webhook integration
• Gotify - Self-hosted push notification service
• Join - Cross-device notification service

Updated Channel Lists

• Updated channels/index.md to include all 19 services (added 4 new ones)
• Updated reference/notifications/index.mdx to include Generic Webhook
• Fixed typo: Shoutrr → Shoutrrr
• Fixed Shoutrrr documentation link: v0.7 → v0.8

Event Documentation

• Added missing config events: config.changed and config.degraded
• Updated YAML example to demonstrate config.changed event usage
• Verified all event types match the source code
• Confirmed incident, component, check, and config events are all documented

Bug Fixes

• Fixed image paths in Google Chat documentation to use relative paths
• All image references now work correctly with Docusaurus build

Code Quality

• All new files pass Vale linting with 0 errors
• Added technical terms to spelling ignore list (apikey, avatarurl, colorDebug, devicekey, joaoapps, subpath)
• Verified YAML examples in fixtures are valid and accurate
• Formatting applied with Prettier

Summary

The notifications documentation is now complete with:

• 19 notification channels fully documented
• All event types from source code covered
• Accurate YAML snippets and examples
• Consistent formatting and styling
• No linting errors in new files
• All image paths corrected for proper build

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update notifications guide</issue_title>
<issue_description>- [ ] Make sure all notification options are document with sane example

• Verify the accuracy of all YAML snippets / enums / etc
• Review notifications in https://github.com/flanksource/mission-control-registry to update examples for</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update notifications guide #426

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[moshloop]

@copilot fix the failing github action checks

[Copilot]

@copilot fix the failing github action checks

Fixed in da4bda6. The issue was incorrect image paths in the Google Chat documentation - they were using absolute paths /img/notifications/channels/googlechat/ instead of relative paths googlechat/ like other channel docs. The build should now pass.