Generates the Ecto migration that creates Continuum's Postgres tables.
mix continuum.gen.migrationWrites a single migration file under priv/repo/migrations/ (or whatever
is configured for your repo) that creates: continuum_runs,
monthly-partitioned continuum_events, continuum_signals,
continuum_timers, continuum_activity_tasks,
continuum_activity_results, continuum_snapshots,
continuum_workflow_versions, and the continuum_lease_token_seq sequence.