Add project_id column to p_ci_finished_build_ch_sync_events

What does this MR do and why?

This MR adds a project_id column to p_ci_finished_build_ch_sync_events to serve as a sharding key for Cells 1.0. The column will have a default value of -1 (irrelevant right now since we'll only use this value later on in Cells 1.0, and these records have a maximum lifetime of 30 days).

• EE: true
• Changelog: added

Part of #459997 (closed)

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