Investigate migrating `PipelineAnalytics` from `ci_finished_pipelines` MVs to `siphon_p_ci_pipelines`

Context

p_ci_pipelines is now fully replicated to ClickHouse via Siphon as siphon_p_ci_pipelines, with traversal_path populated through the project_traversal_paths_dict dictionary.

Today, PipelineAnalytics (project + group GraphQL field) reads from two AggregatingMergeTree materialized views — ci_finished_pipelines_hourly and ci_finished_pipelines_daily — built on the raw ci_finished_pipelines table, which is CSV-synced from Postgres by Ci::ClickHouse::DataIngestion::FinishedPipelinesSyncService.

This issue tracks a feasibility analysis and (if green-lit) execution of switching the data source to Siphon synced tables, so we can retire the bespoke sync pipeline. (gitlab.com first)