[exporter/splunk_hec] Batch by resource attributes index and access token

[atoulme]

Component(s)

exporter/splunkhec

Is your feature request related to a problem? Please describe.

The Splunk HEC exporter gets a 400 error on sending batches if at least one element in the batch has a bad index value.

The fix is to batch per index, so we have a clean way to try batches without partial retries.

Describe the solution you'd like

Batch per index ; we already batch per access token, so batch by both.

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners for exporter/splunkhec: @atoulme @dmitryax. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[crobert-1]

This makes sense to me and was filed by a code owner, removing needs triage.