Fix timestamp inconsistencies beyween PG and CH for Duo Chat Events.

What does this MR do and why?

Recreates duo_chat_events CH table with truncated timestamps. That creates consistency between PG and CH and allows us to leverage ReplacingMergeTree engine. No user facing changes or behavior changes.

References

How to set up and validate locally

1. Migrate CH with bundle exec rake gitlab:clickhouse:migrate
2. In Rails console compare backup table content with new table content. E.g. ClickHouse::Client.select('select * from duo_chat_events', :main)

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #528661