Fix metric name capturing in annotations

[GiedriusS]

In a lot of places now we add annotations but we don't capture the metric name anywhere because it's not part of the operator. Probably need to capture the metric name once and then pass it down to the surrounding operators.

[MichaHoffmann]

Operators have the Series() method - that and the series id should be enough to get all labels - some won't have metric name anymore though because of prior aggregations but for those it would be unclear what the metric name is even I think.