[Tooling] Add google owned cache for dependencies as an option in ci

GRADLE_STRUCTURE.md

@@ -0,0 +1,16 @@
+# Gradle Structure
+
+`package/example/android/settings.gradle` imports the flutter tooling and includes the `app` directory and it configures GoogleCloudPlatform/artifact-registry-maven-tools for use in ci.
+
+This repo has a GCP instance that mirrors dependencies available from `google()` and `mavenCentral()` used by ci (or googlers). This gives us redudent uptime for dependency availability.
+
+Using this cache is not intended or avaiable for contributors outside of CI. We protect that execution with an environment variable ARTIFACT_HUB to ensure that by default users do not see rejected cloud credentials or errors in builds.
+
+Googlers can debug locally by setting ARTIFACT_HUB to the valid artifact hub value and authenticating with GCP. To authenticate run `gcloud auth application-default login`. To find artifact hub url use `<url>` section of go/artifact-hub#maven or inspect the value on CI servers. CI uses a service account for billing. That is defined in go/artifact-hub-service-account (googler access only).
+
+## Useful links for debuging
+https://github.com/GoogleCloudPlatform/artifact-registry-maven-tools/blob/master/README.md
+https://docs.gradle.org/current/userguide/declaring_repositories.html
+https://docs.gradle.org/current/userguide/viewing_debugging_dependencies.html
+
+Comamnd to force refresh of dependencies `./gradlew app:dependencies --configuration <SOME_TASK> --refresh-dependencies`

packages/camera/camera_android_camerax/example/android/build.gradle

@@ -16,6 +16,11 @@ buildscript {
 
 allprojects {
     repositories {
+        // See GRADLE_STRUCTURE.md for more info.
+        if (System.getenv().containsKey('ARTIFACT_HUB')) {
+            println "Using artifact hub"
+            maven { url System.getenv('ARTIFACT_HUB') }
+        }
         google()
         mavenCentral()
     }

packages/camera/camera_android_camerax/example/android/settings.gradle

@@ -9,3 +9,16 @@ localPropertiesFile.withReader("UTF-8") { reader -> properties.load(reader) }
 def flutterSdkPath = properties.getProperty("flutter.sdk")
 assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
 apply from: "$flutterSdkPath/packages/flutter_tools/gradle/app_plugin_loader.gradle"
+
+// See GRADLE_STRUCTURE.md for more info.
+buildscript {
+  repositories {
+    maven {
+      url "https://plugins.gradle.org/m2/"
+    }
+  }
+  dependencies {
+    classpath "gradle.plugin.com.google.cloud.artifactregistry:artifactregistry-gradle-plugin:2.2.1"
+  }
+}
+apply plugin: "com.google.cloud.artifactregistry.gradle-plugin"