added build script

Author: psinghbay1

build.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+git remote add upstream https://github.com/googleapis/java-spanner.git
+git pull upstream main --no-rebase
+
+mvn com.coveo:fmt-maven-plugin:format
+mvn clean verify