[yaml] add FileIO docs

[Polber]

Add docs for all the FileIO YAML Providers. This includes separating out the providers into standalone function calls rather than using a remaning provider referencing th source transform. This allows for YAML-specific docs and possibe future YAML-specific pre/post processing

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[Polber]

R: @robertwb

[Polber]

R: @damccorm

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[damccorm]

Thanks

[damccorm]

Oh, please fix the precommits

[damccorm]

Looks like precommits are still failing

[codecov]

Codecov Report

Attention: Patch coverage is 60.60606% with 13 lines in your changes missing coverage. Please review.

Project coverage is 57.42%. Comparing base (a9a82a1) to head (c90624e).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
sdks/python/apache_beam/yaml/generate_yaml_docs.py	0.00%	7 Missing ⚠️
sdks/python/apache_beam/yaml/yaml_io.py	76.92%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #33185   +/-   ##
=========================================
  Coverage     57.41%   57.42%           
  Complexity     1474     1474           
=========================================
  Files           970      970           
  Lines        154498   154526   +28     
  Branches       1076     1076           
=========================================
+ Hits          88708    88732   +24     
- Misses        63586    63590    +4     
  Partials       2204     2204           

Flag	Coverage Δ
python	81.40% <60.60%> (+<0.01%)	⬆️

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[robertwb]

I'm not sure we want to go this direction; re-using the docs from the original transforms rather than duplicating them is a feature, not a bug. Certainly they could be improved (which would improve both).

[robertwb]

We can't always filter these out, e.g. https://beam.apache.org/releases/yamldoc/current/#pytransform

[Polber]

Ah.. right.. let me rethink

[robertwb]

Note that we support more than local files and gcs; the set of filesystems is not closed.

[Polber]

Right, I also found that limiting, but I copied that description from another docstring, e.g.

beam/sdks/python/apache_beam/io/textio.py

Lines 757 to 759 in 142e392

	file_pattern (str): The file path to read from as a local file path or a
	GCS ``gs://`` path. The path can contain glob characters
	(``*``, ``?``, and ``[...]`` sets).