feat(web-analytics): Add gad_source to campaign params

[robbie-c]

Changes

Add gad_source to campaign params, to keep in sync with PostHog/posthog#19085

Checklist

• Tests for new code (see advice on the tests we use)
• Accounted for the impact of any changes across different browsers

[github-actions]

Size Change: +52 B (0%)

Total Size: 747 kB

Filename	Size	Change
dist/array.full.js	177 kB	+13 B (0%)
dist/array.js	118 kB	+13 B (0%)
dist/es.js	118 kB	+13 B (0%)
dist/module.js	118 kB	+13 B (0%)

ℹ️ View Unchanged

Filename	Size
dist/exception-autocapture.js	12 kB
dist/recorder-v2.js	104 kB
dist/recorder.js	58.4 kB
dist/surveys.js	41.5 kB

_{compressed-size-action}