Default ci_finished_builds timestamps to zero

What does this MR do and why?

This MR adds clickhouse migrations to default ci_finished_builds timestamps to zero, and change the materialized columns to default to zero, if the values become negative, or started_at is NULL in PG.

Closes #436960 (closed)

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Demo data from prod:

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Run bundle exec rake gitlab:clickhouse:migrate:main

> INSERT INTO ci_finished_builds (id, finished_at) VALUES (9999999, '2023-01-01')
> SELECT id, created_at, queued_at, started_at, finished_at, duration, queueing_duration FROM ci_finished_builds FINAL WHERE id = 9999999

┌──────id─┬─────────────────created_at─┬──────────────────queued_at─┬─────────────────started_at─┬────────────────finished_at─┬─duration─┬─queueing_duration─┐
│ 9999999 │ 1970-01-01 00:00:00.000000 │ 1970-01-01 00:00:00.000000 │ 1970-01-01 00:00:00.000000 │ 2023-01-01 00:00:00.000000 │        0 │                 0 │
└─────────┴────────────────────────────┴────────────────────────────┴────────────────────────────┴────────────────────────────┴──────────┴───────────────────┘