build: map shade.skip across all modules using maven-shade-plugin

Add <skip>${shade.skip}</skip> to maven-shade-plugin configurations in:
- java-bigquery/benchmark
- java-bigtable (and test-proxy)
- java-storage-nio/google-cloud-nio
- java-storage/storage-shared-benchmarking

Author: lqiu96

java-bigquery/benchmark/pom.xml

@@ -61,6 +61,7 @@
               <goal>shade</goal>
             </goals>
             <configuration>
+              <skip>${shade.skip}</skip>
               <finalName>${uberjar.name}</finalName>
               <transformers>
                 <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">

java-bigtable/pom.xml

@@ -286,6 +286,9 @@
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-shade-plugin</artifactId>
                 <version>3.6.0</version>
+                <configuration>
+                    <skip>${shade.skip}</skip>
+                </configuration>
             </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>

java-bigtable/test-proxy/pom.xml

@@ -158,6 +158,7 @@
                 <goal>shade</goal>
               </goals>
               <configuration>
+                <skip>${shade.skip}</skip>
                 <filters>
                   <filter>
                     <artifact>*:*</artifact>

java-storage-nio/google-cloud-nio/pom.xml

@@ -129,6 +129,7 @@
           </dependency>
         </dependencies>
         <configuration>
+          <skip>${shade.skip}</skip>
           <shadedArtifactAttached>true</shadedArtifactAttached>
           <relocations>
             <relocation>

java-storage/storage-shared-benchmarking/pom.xml

@@ -65,6 +65,7 @@
               <goal>shade</goal>
             </goals>
             <configuration>
+              <skip>${shade.skip}</skip>
               <finalName>${uberjar.name}</finalName>
               <transformers>
                 <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">