SIGNL4 Alert Notification

[rons4]

Summary

This PR is to add SIGNL4 mobile alerting as an alert notification integration to Netdata.

I followed the recommendations for contributing alert notifications as mentioned here:
https://github.com/netdata/.github/blob/main/CONTRIBUTING.md

Test Plan

I tested the notifications as described here under "Test Notification":
https://learn.netdata.cloud/docs/alerts-&-notifications/notifications/agent-dispatched-notifications/discord

This was helpful for debugging and it runs fine now (OK states).

Additional Information

SIGNL4 (https://www.signl4.com/) is a mobile alerting service integrating with various tools and Netdata surly belongs here: https://docs.signl4.com/integrations/integrations.html

The idea is to alert responsible users or teams via app push, SMS, or voice call if a critical incident is detected by Netdata. SIGNL4 also includes escalations, on-call scheduling and in-alert collaboration.

For users: How does this change affect me?

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
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[ilyam8]

Hi, @rons4. The .md files will be created from metadata. You don't need to add them.

[rons4]

Thanks, @ilyam8. I saw it but since the .md files were there for the other notification channels I thought I just create the. I have removed them now.

[Copilot]

Pull Request Overview

This PR adds SIGNL4 mobile alerting service as a new notification integration to Netdata. SIGNL4 provides critical alerting via app push, SMS, voice calls, and email with features like tracking, escalation, and on-call scheduling.

• Adds SIGNL4 as a new alert notification method alongside existing integrations
• Implements webhook-based notification delivery to SIGNL4 service
• Provides configuration options for enabling and customizing SIGNL4 notifications

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/health/notifications/signl4/metadata.yaml	Configuration metadata and documentation for SIGNL4 integration
src/health/notifications/health_alarm_notify.conf	Configuration file updates to include SIGNL4 settings and role mappings
src/health/notifications/alarm-notify.sh.in	Core implementation of SIGNL4 notification sender function

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