chore: add missing hashCodes (googleapis#2630)

Change-Id: I10bfd50174fe2c790aa4a10086a3b14017ba6156

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Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: igorbernstein2

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/ProtoResultSetMetadata.java

@@ -22,6 +22,7 @@
 import com.google.cloud.bigtable.data.v2.models.sql.ColumnMetadata;
 import com.google.cloud.bigtable.data.v2.models.sql.ResultSetMetadata;
 import com.google.cloud.bigtable.data.v2.models.sql.SqlType;
+import com.google.common.base.Objects;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import java.util.List;
@@ -94,4 +95,9 @@ public boolean equals(@Nullable Object other) {
     }
     return false;
   }
+
+  @Override
+  public int hashCode() {
+    return Objects.hashCode(columns);
+  }
 }

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/models/SampleRowKeysRequest.java

@@ -85,4 +85,9 @@ public boolean equals(Object o) {
     SampleRowKeysRequest sampleRowKeysRequest = (SampleRowKeysRequest) o;
     return Objects.equal(targetId, sampleRowKeysRequest.targetId);
   }
+
+  @Override
+  public int hashCode() {
+    return Objects.hashCode(targetId);
+  }
 }