[Feature Request][Go SDK]: Add textio.ReadWithFilename transform

[johannaojeling]

What would you like to happen?

I would like a transform that reads a text file (splittable implementation) and emits the file path paired with each line, i.e. returns a PCollection<KV<string, string>>

Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

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[johannaojeling]

.take-issue