Add custom User-Agent header support for Mattermost integration

[ckaytev]

Summary

This PR adds the ability to override the default User-Agent header for Mattermost API requests.

Problem

Many enterprise environments deploy WAF solutions that automatically block or flag requests containing default HTTP client user agents (e.g., python-requests, python/3.12). This causes Robusta's Mattermost integration to fail in such environments, preventing alert notifications from being delivered.

By allowing users to customize the User-Agent header, Robusta can now work seamlessly in environments with strict WAF policies.

Configuration Example

sinksConfig:
- mattermost_sink:
    name: mattermost_sink
    url: https://mattermost.example.com
    token: <YOUR_BOT_TOKEN>
    token_id: <YOUR_BOT_TOKEN_ID>
    channel: alerts
    user_agent: "Robusta/1.0"  # Optional: custom User-Agent to bypass WAF

Backward Compatibility

This change is fully backward compatible. The user_agent parameter is optional and defaults to None. When not specified, the behavior remains unchanged (no custom User-Agent header is set, and the underlying HTTP client uses its default).

Testing

• Verified that existing Mattermost integrations work without specifying user_agent
• Tested custom User-Agent header is properly sent when configured

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: f7b9d1b5-1bec-4838-a794-0cf209f37853

📥 Commits

Reviewing files that changed from the base of the PR and between 7c8d299 and 9f8c60d.

📒 Files selected for processing (4)

• docs/configuration/sinks/mattermost.rst
• src/robusta/core/sinks/mattermost/mattermost_sink.py
• src/robusta/core/sinks/mattermost/mattermost_sink_params.py
• src/robusta/integrations/mattermost/client.py

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Walkthrough

This pull request adds optional user_agent parameter support to the Mattermost sink. The parameter flows through the configuration schema, sink initialization, and Mattermost client, where it is conditionally included as a User-Agent header in API requests.

Changes

Cohort / File(s)	Summary
Documentation docs/configuration/sinks/mattermost.rst	Added user_agent field to the Mattermost sink configuration example in generated_values.yaml.
Configuration Schema src/robusta/core/sinks/mattermost/mattermost_sink_params.py	Added optional user_agent: Optional[str] field to MattermostSinkParams.
Implementation src/robusta/core/sinks/mattermost/mattermost_sink.py, src/robusta/integrations/mattermost/client.py	Updated MattermostSink to pass user_agent from config to MattermostClient constructor; enhanced MattermostClient to accept user_agent parameter and conditionally add User-Agent header to outgoing API requests.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 16.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: adding custom User-Agent header support for Mattermost integration.
Description check	✅ Passed	The description clearly explains the problem, solution, configuration example, backward compatibility, and testing performed—all directly related to the changeset.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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