Add types to api/__init__.py

This is a **temporary** fix to make tests pass

Author: smokestacklightnin

tensorflow_model_analysis/api/__init__.py

@@ -11,3 +11,8 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from tensorflow_model_analysis.api import types
+
+__all__ = [
+    "types",
+]