SGM-6931 - A/B test header on the /Cody page #2

[gitstart-app[bot]]

This PR was created by GitStart to address the requirements from this ticket: SGM-6931. This ticket was imported from: SGM-6931

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DESCRIPTION:

Displays Different header on the Cody page depending on User group

Figma Design: https://www.figma.com/file/oQgh5R0iSBG3UII6C8CPJ8/Cody-page?type=design&node-id=4582-14344&mode=dev

Ensures pageloads after the feature flag from PostHog is loaded

• "control" group members, see section:

"Cody is a coding AI assistant that uses AI and a deep understanding of your codebase to help you write and understand code faster."

• "test" group members, see section

"Cody is the AI coding assistant that understands your code.

• Ingest Code from any code host
• Choose from the latest AI models
• Get relevant AI suggestions through enhanced context"

• While "undefined" group members (in the case PostHog fails), see the same headline as "control" group members.
• When a user lands on the Cody page, it logs an enrollment event to eventLogger. With name: ValueHeadlineTestEnrolledand adds user's variant in the event metadata "Control" or "Test"

REF:

• [Sourcegraph Issue] https://github.com/sourcegraph/about/issues/6931
• [Ticket] (https://clients.gitstart.com/sourcegraph/3436/tickets/SGM-6931)

DEMO:

https://www.loom.com/share/56b72ba281b3438b8b15c57c6884aec5?sid=b00d5da6-51c6-470e-92e1-01fa53736783

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[gitstart-sourcegraph]

Hi @iskyOS This PR cherrypicks only relevant file changes from this PR as requested. Thank you