nemo2riva: `AttributeError: 'EncDecRNNTBPEModel' object has no attribute 'input_example'`
**Describe the bug**

I'm trying to convert .nemo to .riva, but I'm getting message `AttributeError: 'EncDecRNNTBPEModel' object has no attribute 'input_example`. Converting the Conformer-CTC model is OK but the Conformer-Transducer model cannot.

run command:
```bash
nemo2riva --out model_conformer_transducer.riva Conformer-Transducer-BPE.nemo
```
got following error:
```bash
[NeMo W 2022-08-08 17:31:20 schema:118] Validation schema not found for nemo.collections.asr.models.EncDecRNNTBPEModel.
    That means Riva does not yet support a pipeline for this network and likely will not work with it.
[NeMo I 2022-08-08 17:31:20 artifacts:65] Found model at ./model_weights.ckpt
[NeMo I 2022-08-08 17:31:20 artifacts:143] Retrieved artifacts: dict_keys(['08c8ba770083451b8aad07ed7310d7ef_tokenizer.model', '596cc7598fe44de9a3f4db5f5f5b0a3d_tokenizer.vocab', 'e9aec1bd43144fd3a60e65bee8ae73f2_vocab.txt', 'model_config.yaml'])
[NeMo I 2022-08-08 17:31:20 convert:78] Successfully exported model to model_graph.onnx, saving to model_conformer_transducer.riva ...
[NeMo I 2022-08-08 17:31:20 cookbook:93] Exporting model with autocast=False
[NeMo E 2022-08-08 17:31:20 cookbook:122] ERROR: Export failed. Please make sure your NeMo model class (nemo.collections.asr.models.EncDecRNNTBPEModel) has working export() and that you have the latest NeMo package installed with [all] dependencies.
Traceback (most recent call last):
  File "/opt/conda/bin/nemo2riva", line 8, in <module>
    sys.exit(nemo2riva())
  File "/opt/conda/lib/python3.8/site-packages/nemo2riva/cli/nemo2riva.py", line 56, in nemo2riva
    Nemo2Riva(args)
  File "/opt/conda/lib/python3.8/site-packages/nemo2riva/convert.py", line 79, in Nemo2Riva
    save_archive(model=model, save_path=riva_out, cfg=cfg, artifacts=artifacts, metadata=manifest['metadata'])
  File "/opt/conda/lib/python3.8/site-packages/nemo2riva/cookbook.py", line 123, in save_archive
    raise e
  File "/opt/conda/lib/python3.8/site-packages/nemo2riva/cookbook.py", line 96, in save_archive
    input_example = model.input_module.input_example(**in_args)
  File "/opt/conda/lib/python3.8/site-packages/torch/nn/modules/module.py", line 1204, in __getattr__
    raise AttributeError("'{}' object has no attribute '{}'".format(
AttributeError: 'EncDecRNNTBPEModel' object has no attribute 'input_example'
```


**Steps/Code to reproduce bug**

1. I trained using the config file from:
   - `https://github.com/NVIDIA/NeMo/blob/main/examples/asr/conf/conformer/conformer_transducer_bpe.yaml`
1. When training, .nemo file is saved every epoch.
1. I use .nemo and run it like below:
   - `nemo2riva --out model_conformer_transducer.riva Conformer-Transducer-BPE.nemo`



**Expected behavior**

Convert .nemo to .riva file using `nemo2riva`

**Environment overview (please complete the following information)**

 - Environment location: Docker
 - Method of NeMo install: already installed in Docker image
 - If method of install is [Docker], provide `docker pull` & `docker run` commands used
   - `docker pull nvcr.io/nvidia/nemo:22.05`

docker run command:
```
docker run --runtime=nvidia -it -d --rm \
--gpus '"device=0"' \
-v /home/workspace/NeMo:/root/NeMo \
--shm-size=16g --ulimit memlock=-1 --ulimit stack=67108864 \
--name=nemo_22.05 nvcr.io/nvidia/nemo:22.05
```
**Environment details**

- Docker image : nvcr.io/nvidia/nemo:22.05

I installed additional Python package:
- nemo2riva 2.3.0

If NVIDIA docker image is used you don't need to specify these.
Otherwise, please provide:
- OS version
- PyTorch version
- Python version

**Additional context**

Add any other context about the problem here.
Example: GPU model
