docs: add `nested_type` example in `data_types_and_io/structured_dataset.py`

[austin362667]

Tracking issue

https://github.com/flyteorg/flyte/issues/4241 https://github.com/flyteorg/flytekit/pull/2252 https://github.com/flyteorg/flytesnacks/pull/1657

Why are the changes needed?

Add structured_dataset_nested_type examples in documentation.

https://github.com/flyteorg/flytekit/pull/2252

What changes were proposed in this pull request?

Demonstrate how to use nested_types in structured_dataset

How was this patch tested?

https://github.com/flyteorg/flytekit/pull/2252/files#diff-e78d93a6e6cd2463cd5fc51973434c29ece29d05fe6b36691d6d19860386f938

Setup process

make dev-docs

Screenshots

Check all the applicable boxes

• [ ] I updated the documentation accordingly.
• [ ] All new and existing tests passed.
• [x] All commits are signed-off.

Related PRs

https://github.com/flyteorg/flytekit/pull/2252 https://github.com/flyteorg/flytesnacks/pull/1657

Docs link

https://docs.flyte.org/en/latest/user_guide/data_types_and_io/structureddataset.html#structured-dataset

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 61.10%. Comparing base (5cfd004) to head (d6230d5). Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5269   +/-   ##
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  Coverage   61.10%   61.10%           
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  Files         794      794           
  Lines       51213    51213           
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  Hits        31295    31295           
  Misses      17037    17037           
  Partials     2881     2881           

Flag	Coverage Δ
unittests-datacatalog	69.31% <ø> (ø)
unittests-flyteadmin	58.90% <ø> (ø)
unittests-flytecopilot	17.79% <ø> (ø)
unittests-flytectl	68.30% <ø> (ø)
unittests-flyteidl	79.30% <ø> (ø)
unittests-flyteplugins	61.94% <ø> (ø)
unittests-flytepropeller	57.32% <ø> (ø)
unittests-flytestdlib	65.75% <ø> (ø)

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