change bucket type to string (#894)

cmd/hack/hack.go

cmd/integration/commands/refetence_db.go

cmd/pics/state.go

cmd/state/commands/check_index.go

cmd/state/commands/index_stats.go

cmd/state/commands/regenerate_index.go

cmd/state/generate/regenerate_index.go

cmd/state/stateless/state.go

cmd/state/stateless/state_snapshot.go

cmd/state/stateless/state_snapshot_test.go

cmd/state/stateless/witness_db.go

cmd/state/stats/index_stats.go

cmd/state/verify/check_indexes.go

common/changeset/changeset.go

common/dbutils/bucket.go

common/dbutils/composite_keys.go

common/dbutils/helper.go

common/dbutils/history_index.go

common/etl/collector.go

common/etl/etl.go