Add google maven mirror to repositories.

Author: shunping

buildSrc/build.gradle.kts

@@ -26,6 +26,7 @@ plugins {
 // Define the set of repositories required to fetch and enable plugins.
 repositories {
   maven { url = uri("https://plugins.gradle.org/m2/") }
+  maven { url = uri("https://maven-central.storage-download.googleapis.com/maven2/") }
   maven {
     url = uri("https://repo.spring.io/plugins-release/")
     content { includeGroup("io.spring.gradle") }

buildSrc/src/main/groovy/org/apache/beam/gradle/Repositories.groovy

@@ -37,6 +37,7 @@ class Repositories {
       }
 
       mavenCentral()
+      maven { url "https://maven-central.storage-download.googleapis.com/maven2/" }
       mavenLocal()
 
       // For Confluent Kafka dependencies
@@ -69,6 +70,7 @@ class Repositories {
       repositories {
         mavenLocal()
         mavenCentral()
+        maven { url "https://maven-central.storage-download.googleapis.com/maven2/" }
         maven { url "https://plugins.gradle.org/m2/" }
         maven { url "https://repo.spring.io/plugins-release" }
         maven { url "https://packages.confluent.io/maven/" }