Combine price feed transformers

- fetches logs from all three price feeds in one query
- assumes eth/usd price feed will be updated to include LogValue event
- updates transformers to run separate from header sync

pkg/datastore/postgres/repositories/header_repository.go

@@ -3,6 +3,7 @@ package repositories
 import (
 	"database/sql"
 	"errors"
+
 	"github.com/vulcanize/vulcanizedb/pkg/core"
 	"github.com/vulcanize/vulcanizedb/pkg/datastore/postgres"
 )