feat: add irclid and _kx as campaign parameters

[havenbarnes]

Changes

Context: posthoghelp.zendesk.com/agent/tickets/22717

User requested we support campaign URL params from the Impact and Klaviyo platforms; this seems trivially cheap and straightforward for us to support.

Paired with PostHog/posthog#27485

Checklist

• Tests for new code (see advice on the tests we use)
• Accounted for the impact of any changes across different browsers
• Accounted for backwards compatibility of any changes (no breaking changes in posthog-js!)

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Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Jan 13, 2025 11:21pm

[github-actions]

Size Change: +165 B (+0.01%)

Total Size: 3.23 MB

Filename	Size	Change
dist/array.full.es5.js	264 kB	+15 B (+0.01%)
dist/array.full.js	366 kB	+15 B (0%)
dist/array.full.no-external.js	365 kB	+15 B (0%)
dist/array.js	180 kB	+15 B (+0.01%)
dist/array.no-external.js	179 kB	+15 B (+0.01%)
dist/customizations.full.js	12.6 kB	+15 B (+0.12%)
dist/main.js	181 kB	+15 B (+0.01%)
dist/module.full.js	366 kB	+15 B (0%)
dist/module.full.no-external.js	365 kB	+15 B (0%)
dist/module.js	180 kB	+15 B (+0.01%)
dist/module.no-external.js	179 kB	+15 B (+0.01%)

ℹ️ View Unchanged

Filename	Size
dist/all-external-dependencies.js	207 kB
dist/dead-clicks-autocapture.js	14.4 kB
dist/exception-autocapture.js	9.48 kB
dist/external-scripts-loader.js	2.64 kB
dist/recorder-v2.js	115 kB
dist/recorder.js	115 kB
dist/surveys-preview.js	58.1 kB
dist/surveys.js	63.8 kB
dist/tracing-headers.js	1.76 kB
dist/web-vitals.js	10.4 kB

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