Collection fails on billing emitter error

[jml]

Elsewhere, @bboreham states:

I think the scope collector should continue to function even when billing is down.

A quick search through the scope code shows

scope/app/multitenant/billing_emitter.go

Lines 82 to 87 in 860dfb7

	if err != nil {
	log.Errorf("Failed emitting billing data: %v", err)
	return err
	}
	return e.Collector.Add(ctx, rep, buf)

There, BillingEmitter (a decorator around the Collector interface) will only call the "upstream" collector if it successfully emitted billing details.

We could change it to forward even on emitter failure, or we could shift the model from decorator to composite, using something to tee reports to both destinations in parallel. No doubt there are other options too.