docs(v1): use posthog instead of segment

[shahednasser]

• Use posthog in v1 docs
• Remove segment usage from v1 docs
• Add note to deployment guides

Closes DX-2274

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Latest commit: 2014209

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Project	Deployment	Preview	Comments	Updated (UTC)
api-reference	Building	Preview	Comment	Nov 4, 2025 0:36am
api-reference-v2	Error			Nov 4, 2025 0:36am
cloud-docs	Error			Nov 4, 2025 0:36am
docs-ui	Error			Nov 4, 2025 0:36am
docs-v2	Error			Nov 4, 2025 0:36am
medusa-docs	Error			Nov 4, 2025 0:36am
resources-docs	Error			Nov 4, 2025 0:36am
user-guide	Error			Nov 4, 2025 0:36am