[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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