Adds the composite indexes that the generated Oban triggers need, for resources using AshPostgres.DataLayer.

Every generated trigger filters on state, and every timeout trigger also filters on its field. ago/2 compiles to a bind parameter rather than a per-row function call, so a timeout's where reaches Postgres as state = $1 AND state_entered_at <= $2 — an ordinary composite range scan. Without an index that is a sequential scan on every poll, for every timeout.

Indexes are named ash_workflow_<table>_<fields>_index so they are recognisable in migrations as belonging to this extension, and are only added when no existing custom_indexes entry already covers the same fields — a user-declared index always wins.

Resources on other data layers are untouched; see AshWorkflow.Info.recommended_indexes/1 for the same information as data.

Opt out per resource with workflow do generate_indexes? false end.