PoC for efficient querying of ci_build wait time per group from ClickHouse

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POC for ci analytics on ClickHouse (!126863 - closed) were centered around instance-wide view of ci_builds wait times, we want to implement similar views/queries on the group level.

This is challenging and requires some more research.

Potential approaches:

1. just filtering by project_id IN () (this may read large amount of data and require optimization, needs testing)
2. adding a separate table for project hierarchy using the CollapsingMergeTree/VersionedCollapsingMergeTree engines and creating special materialized views based on joining finished_ci_builds and that heirarchy table