Add recipe for OCR task on IAM handwriting dataset

[kenzheng99]

Current best performance is about 6.8 CER, which is still a bit off from SOTA results on this dataset. Let me know if anyone has suggestions for further performance tuning of this recipe.

[sw005320]

Please fix https://github.com/espnet/espnet/actions/runs/3323163660/jobs/5524495069#step:8:8669

[codecov]

Codecov Report

Merging #4707 (2169367) into master (143c946) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4707      +/-   ##
==========================================
+ Coverage   80.31%   80.32%   +0.01%     
==========================================
  Files         527      527              
  Lines       46311    46311              
==========================================
+ Hits        37193    37200       +7     
+ Misses       9118     9111       -7     

Flag	Coverage Δ
test_integration_espnet1	66.37% <ø> (+0.13%)	⬆️
test_integration_espnet2	48.96% <ø> (+0.11%)	⬆️
test_python	68.56% <ø> (ø)
test_utils	23.30% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
espnet/tts/pytorch_backend/tts.py	78.63% <0.00%> (+0.29%)	⬆️
...et/nets/pytorch_backend/e2e_asr_mix_transformer.py	84.97% <0.00%> (+0.46%)	⬆️
espnet/asr/asr_utils.py	76.53% <0.00%> (+0.87%)	⬆️
...pnet/nets/pytorch_backend/transformer/optimizer.py	88.88% <0.00%> (+2.77%)	⬆️

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[ftshijt]

Very cool PR! Could you please also update the corresponding entry in egs2/TEMPLATE/README.md

[mergify]

This pull request is now in conflict :(

[sw005320]

@kenzheng99, could you reflect @ftshijt's comments?

[sw005320]

Can you add a pre-trained model?

[mergify]

This pull request is now in conflict :(

[sw005320]

Please reflect the comments ($IAM issue and model upload).

[kenzheng99]

Updated the last comment! For model upload, I have just made a HuggingFace account (username is kenzheng99) and requested access to the ESPnet org, once I get that I can upload my model.

[ftshijt]

Updated the last comment! For model upload, I have just made a HuggingFace account (username is kenzheng99) and requested access to the ESPnet org, once I get that I can upload my model.

Very cool! You can make a separate PR for the update of the link. Will merge this PR. Many thanks for your contribution!