gcp-csm-o11y: Use xds's shadow configuration

This prevents mixing shaded and non-shaded class files. We do the same
thing in all the other projects that depend on xds.

gcp-csm-observability/build.gradle

@@ -18,7 +18,7 @@ dependencies {
             project(':grpc-core'),
             project(':grpc-opentelemetry'),
             project(':grpc-protobuf'),
-            project(':grpc-xds'),
+            project(path: ':grpc-xds', configuration: 'shadow'),
             libraries.guava.jre, // jre version pulled in via xds
             libraries.protobuf.java,
             libraries.opentelemetry.gcp.resources,