Extend unique-visitors endpoint with includeConverting param

[freddyDOTCMS]

Description

Extend GET /v1/analytics/event/unique-visitors with a new optional query parameter includeConverting=true. When present, the response also includes uniqueConvertingVisitors — the count of visitors with at least one conversion event. This is a fully backward-compatible addition.

Improvement plan: https://docs.google.com/document/d/1hVfIurPqAJJ1PN1EalmvrWXnGNt5sY21MI-409lrXpU/edit?tab=t.klqavlz4cis7#heading=h.8vek9yxwq8yt

Parent epic: #35048

Endpoint

GET /v1/analytics/event/unique-visitors

Query parameters

Param	Required	Description
siteId	✅	dotCMS site identifier
eventType	✅	Event type filter
from + to OR range	✅	Time range (absolute or relative)
clusterId	✅	Environment identifier
includeConverting	❌	When true, include uniqueConvertingVisitors in response

Headers

Header	Description
X-Customer-Id	Customer identifier
X-Signature	HMAC-SHA256 signature

Time range rules

• If from/to are present → use them, ignore range
• Else if range is present → compute from/to

Acceptance Criteria

• includeConverting optional param added to GET /v1/analytics/event/unique-visitors
• When includeConverting=true: response includes uniqueConvertingVisitors (visitors with ≥1 conversion event)
• When includeConverting is absent or false: response is unchanged (backward compatible)
• Mandatory params validated: siteId, eventType, time range, clusterId
• Time range rules applied correctly (absolute takes precedence over relative)
• Tests cover: with flag, without flag, missing mandatory params

Additional Context

• Source task: Conversion Endpoint Detail changes — existing endpoint extension
• Requires Phase 2 completion (UA parser, parsed_ua_* columns populated) — blocked by: Update ClickHouse Materialized Views after lookup table removal #35062
• Related branch: issue-34849-Add-dotCMS-Analytics-Proxy-Endpoint-for-/v1/analytics/-to-dot-ca-event-manager