fix: default to PickFirstLoadBalancerProvider (GoogleCloudPlatform#2063)

The services/META-INF/io.grpc.LoadBalancerProvider file included by
default in the jar with dependencies did not correspond with the
default pick_first policy of AutoConfiguredLoadBalancerFactory.

Fixes GoogleCloudPlatform#2061

Co-authored-by: Les Vogel <lesv@users.noreply.github.com>

spanner/cloud-client/assembly-descriptor.xml

@@ -0,0 +1,27 @@
+<assembly xmlns="http://maven.apache.org/ASSEMBLY/2.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/ASSEMBLY/2.0.0 http://maven.apache.org/xsd/assembly-2.0.0.xsd">
+    <id>jar-with-dependencies</id>
+    <formats>
+        <format>jar</format>
+    </formats>
+    <includeBaseDirectory>false</includeBaseDirectory>
+    <dependencySets>
+        <dependencySet>
+            <outputDirectory>/</outputDirectory>
+            <useProjectArtifact>false</useProjectArtifact>
+            <unpack>true</unpack>
+            <unpackOptions>
+                <excludes>
+                    <exclude>io.grpc.LoadBalancerProvider</exclude>
+                </excludes>
+            </unpackOptions>
+        </dependencySet>
+    </dependencySets>
+    <fileSets>
+        <fileSet>
+            <directory>${project.build.outputDirectory}</directory>
+            <outputDirectory>.</outputDirectory>
+        </fileSet>
+    </fileSets>
+</assembly>

spanner/cloud-client/pom.xml

@@ -146,9 +146,9 @@ limitations under the License.
         <artifactId>maven-assembly-plugin</artifactId>
         <version>3.2.0</version>
         <configuration>
-          <descriptorRefs>
-            <descriptorRef>jar-with-dependencies</descriptorRef>
-          </descriptorRefs>
+          <descriptors>
+            <descriptor>assembly-descriptor.xml</descriptor>
+          </descriptors>
           <archive>
             <manifest>
               <mainClass>com.example.spanner.SpannerSample</mainClass>

spanner/cloud-client/src/main/resources/META-INF/services/io.grpc.LoadBalancerProvider

@@ -0,0 +1 @@
+io.grpc.internal.PickFirstLoadBalancerProvider