samples: add samples for statistics package (#1239)

Adds samples for client with query options and query with query options
specifying the optimizer statistics package.

Author: thiagotnunes

samples/snippets/src/main/java/com/example/spanner/SpannerSample.java

@@ -1507,7 +1507,11 @@ static void clientWithQueryOptions(DatabaseId db) {
     SpannerOptions options =
         SpannerOptions.newBuilder()
             .setDefaultQueryOptions(
-                db, QueryOptions.newBuilder().setOptimizerVersion("1").build())
+                db, QueryOptions
+                    .newBuilder()
+                    .setOptimizerVersion("1")
+                    .setOptimizerStatisticsPackage("auto_20191128_14_47_22UTC")
+                    .build())
             .build();
     Spanner spanner = options.getService();
     DatabaseClient dbClient = spanner.getDatabaseClient(db);
@@ -1531,7 +1535,11 @@ static void queryWithQueryOptions(DatabaseClient dbClient) {
             .executeQuery(
                 Statement
                     .newBuilder("SELECT SingerId, AlbumId, AlbumTitle FROM Albums")
-                    .withQueryOptions(QueryOptions.newBuilder().setOptimizerVersion("1").build())
+                    .withQueryOptions(QueryOptions
+                        .newBuilder()
+                        .setOptimizerVersion("1")
+                        .setOptimizerStatisticsPackage("latest")
+                        .build())
                     .build())) {
       while (resultSet.next()) {
         System.out.printf(