feat(snuba): Add ConditionalFormula to Column proto for EAP queries

[phacops]

Add support for conditional expressions in EAP queries by introducing
ConditionalFormula and FormulaCondition message types to the Column proto.

This enables use cases like calculating hourly event rates with different
formulas based on aggregate values:

if(min(timestamp) < one_week_ago,
   count(*) / 168,                    -- use full week for old issues
   count(*) / hours_since_first_seen) -- use actual hours for new issues

Changes:

• Add ConditionalFormula message with condition, match, and default fields
• Add FormulaCondition message with comparison operators (left, op, right)
• Add conditional_formula as field 7 in the Column oneof

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	⏩ skipped	✅ passed	✅ passed	Jan 30, 2026, 10:45 PM