feat(kafka): enqueue commit offset only once per batch process

[cyriltovena]

What this PR does / why we need it:

This ensure we enqueue commit in ingester only once we have processed the batch and not when it was sent to the channel for processing which could cause dataloss if the ingester crashes in between

Which issue(s) this PR fixes:
Fixes https://github.com/grafana/loki-private/issues/1123

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[grobinson-grafana]

Wouldn't this be the same (we don't need the manual step at the start before the backoff loop)?

func retryWithBackoff(ctx context.Context, fn func(attempts int) error) error {
    backoff := backoff.New(ctx, backoff.Config{
		MinBackoff: 100 * time.Millisecond,
		MaxBackoff: 5 * time.Second,
		MaxRetries: 0, // Retry infinitely
	})
    for backoff.Ongoing() {
		err = fn(backoff.NumRetries())
		if err == nil {
			return nil
		}
		if !canRetry(err) {
			return err
		}
		backoff.Wait()
	}
}

[cyriltovena]

I'm actually avoiding the backoff creation for every record in case its all fine.

[cyriltovena]

Might be over-optimization ?