Makefile: implement make db-tests

enables the option to run the DB tests locally
that are executed in the github actions

tools/dbtest-prepare-env.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+pushd $(mktemp -d)
+go mod init temp
+go install github.com/jackc/tern@latest
+popd