HTTP2 errors with ingestion

[gordallott]

http2: Transport: cannot retry err [http2: Transport received Server's graceful shutdown GOAWAY] after Request.Body was written; define Request.GetBody to avoid this error

Solved by setting request.GetBody(), axiom-go would need to provide an additional ingest api, something like

client.IngestStream(ctx, "my-dataset", func() (io.ReadCloser, error) {
	return os.Open("/some/file")
})

so that the go http client can retry correctly