Default SchemaTransform configs to snake_case

[ahmedabu98]

Bringing back the changes reverted in #31109

More details in #31061 and #31353

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[ahmedabu98]

R: @robertwb
R: @chamikaramj

CC: @lostluck (if this affects Go at all)
CC: @Polber (if any more changes are needed for YAML)

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[ahmedabu98]

Fixes #31353

[lostluck]

Probably does affect Go, but IIRC it just means non idiomatic go field names in generated structs. The existing schema handling code should handle making sure the field is Exported (upper case first character) with a manual field name override of the given snake case name.

[ahmedabu98]

Thanks for the insight @lostluck! From a cursory search I see xlang/bigtableio/bigtableio.go is currently the only SchemaTransform use-case in the Go SDK, is that right?

[ahmedabu98]

R: @lostluck

manual field name override of the given snake case name.

let me know if the last commit does what you meant here

[lostluck]

Thanks for the insight @lostluck! From a cursory search I see xlang/bigtableio/bigtableio.go is currently the only SchemaTransform use-case in the Go SDK, is that right?

I have no idea. I do not keep track of cross language implementations and details about specific IOs. Your search would be as good as mine.

[Polber]

Left some comments

[ahmedabu98]

Thanks @Polber for catching those, can you PTAL again?

[Polber]

@ahmedabu98 LGTM, but there is an open PR #31455 that would require a couple changes as well if it gets in before this PR is merged

[robertwb]

@chamikaramj would this impact using the transform service cross-version?

[chamikaramj]

So transform service just wrap expansion services. So change of behavior should be similar to the change of behavior of the Java expansion service.

Regarding, cross-version usage, I think what could break is use-cases that assume a schema from a old Beam version while trying to use the new Beam version for expansion. For example, hand-coded wrappers in customer's side. We are updating the affected Beam provided wrappers so I think the chances of someone running into issues due to this should be rare.