all: make indexer configurable (#17188)

core/chain_indexer.go

eth/backend.go

eth/bloombits.go

les/api_backend.go

les/backend.go

les/bloombits.go

les/commons.go

les/handler.go

les/handler_test.go

les/helper_test.go

les/odr.go

les/odr_requests.go

les/odr_test.go

les/peer.go

les/request_test.go

les/server.go

light/lightchain.go

light/lightchain_test.go

light/odr.go

light/odr_test.go