Add a maven/configure-mirror pipeline to redirect to GCP.

We've seen some slowness and flakiness on GCP runners when
hitting maven central. Configuring this is tricky, so I made a pipeline.

Signed-off-by: Dan Lorenc <dlorenc@chainguard.dev>

pkg/build/pipelines/maven/configure-mirror.yaml

@@ -0,0 +1,20 @@
+name: Configure GCP Maven Central mirror for faster downloads
+needs:
+  packages:
+    - busybox
+pipeline:
+  runs: |
+    # Maven checks $USER/.m2, we set $HOME to /home/build but it hardcodes $USER somehow
+    mkdir -p /root/.m2
+    cat > /root/.m2/settings.xml <<EOF
+      <settings>
+        <mirrors>
+          <mirror>
+            <id>google-maven-central</id>
+            <name>GCS Maven Central mirror</name>
+            <url>https://maven-central.storage-download.googleapis.com/maven2/</url>
+            <mirrorOf>*</mirrorOf>
+          </mirror>
+        </mirrors>
+      </settings>
+    EOF