transform-sdk/go: introduce RecordWriter

[rockwotj]

We've recieved good feedback that a more idiomatic interface for
transforms is using a pattern similar to http.HandlerFunc. This is much
cleaner IMO and allows for emitting records without buffering, as slices
are sometimes akward to work with.

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v23.3.x
• v23.2.x
• v23.1.x

Release Notes

Improvements

• Data Transforms written in Golang now use a non-buffered write mechanism. Transforms that used to be written as

  func myTransform(e transform.WriteEvent) ([]transform.Record, error) {
    return transform.Record[]{e.Record()}, nil
  }
  

  Can now be written as

  func myTransform(e transform.WriteEvent, w transform.RecordWriter) error {
    return w.Write(e.Record())
  }
  

[cohix]

Love this 👍🏼

[oleiman]

lgtm

[vbotbuildovich]

/backport v23.3.x