Initialize int8 migration for ci_builds

What does this MR do?

Related issue: #325618 (closed)

This initializes the int8 migration for ci_builds. We target two columns: id, stage_id to migrate from int4 to int8:

1. Add new columns
2. Install triggers
3. Backfill existing data for .com and dev/test

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content