feat: add UTM parameter tracking for new user signups

[wunderhawk]

• Read UTM cookies (utm_source, utm_medium, utm_campaign, utm_content, utm_term) from request headers
• Include UTM parameters in USER_REGISTER_SUCCESS webhook payload
• Update PlatformWebhookService User interface to support optional UTM fields

https://linear.app/wundergraph/issue/ENG-8867/feat-pass-utm-tags-to-ac-upon-cosmo-sign-up

Summary by CodeRabbit

• New Features
  • Platform webhooks now include UTM campaign attribution data (source, medium, campaign, content, and term) in user registration events. These parameters are automatically captured from cookies and forwarded with webhook payloads, enabling improved tracking of user acquisition sources, marketing channel performance, and overall campaign effectiveness across your connected systems and integrations.

[coderabbitai]

Walkthrough

This PR adds UTM parameter tracking to the user registration webhook. It parses utm_source, utm_medium, utm_campaign, utm_content, and utm_term from cookies during user registration and includes these values in the USER_REGISTER_SUCCESS platform webhook payload.

Changes

Cohort / File(s)	Summary
Authentication UTM Enrichment controlplane/src/core/controllers/auth.ts	Adds extraction of five UTM parameters from cookies and includes them in the USER_REGISTER_SUCCESS webhook payload upon new user registration.
Webhook Payload Schema controlplane/src/core/webhooks/PlatformWebhookService.ts	Extends the User interface with five optional UTM-related properties (utm_source, utm_medium, utm_campaign, utm_content, utm_term) to support the enriched webhook payload.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• feat: preserve tracking cookies #2319: Implements middleware to set and preserve UTM tracking cookies, which are read and forwarded by this PR's webhook payload enrichment.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'feat: add UTM parameter tracking for new user signups' directly and clearly summarizes the main change: adding UTM tracking to user registration.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing touches

• 📝 Generate docstrings

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[codecov]

Codecov Report

❌ Patch coverage is 8.33333% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.30%. Comparing base (f585037) to head (71ba143).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
controlplane/src/core/controllers/auth.ts	8.33%	11 Missing ⚠️

❌ Your patch check has failed because the patch coverage (8.33%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2488      +/-   ##
==========================================
+ Coverage   61.63%   63.30%   +1.66%     
==========================================
  Files         229      296      +67     
  Lines       23894    41698   +17804     
  Branches        0     4391    +4391     
==========================================
+ Hits        14728    26395   +11667     
- Misses       7924    15281    +7357     
+ Partials     1242       22    -1220     

Files with missing lines	Coverage Δ
...lplane/src/core/webhooks/PlatformWebhookService.ts	53.84% <ø> (ø)
controlplane/src/core/controllers/auth.ts	9.56% <8.33%> (ø)

... and 523 files with indirect coverage changes

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