Fix tag propagation for temporal functions (#1307)

Temporal functions don't properly propagate series tags (thanks to @arnikola for suggesting this as the bug!).

For instance, given series:

```
coordinator_engine_datapoints{type="fetched"} 1386
coordinator_engine_datapoints{type="generated"} 104
```

a query like increase(coordinator_engine_datapoints[5s]) will return

```
{
  "__name__": "coordinator_engine_datapoints",
  "instance": "host.docker.internal:7203",
  "job": "coordinator",
  "role": "remote"
}
{
  "__name__": "coordinator_engine_datapoints",
  "instance": "host.docker.internal:7203",
  "job": "coordinator",
  "role": "remote"
}
```

dropping tags. Querying the same range without increase gives all tags, as expected.

Fix is simple; we weren't copying tags into the new block's SeriesMetas; now we do.

src/query/functions/temporal/base.go

@@ -254,10 +254,16 @@ func (c *baseNode) processSingleRequest(request processRequest) error {
 	bounds := seriesIter.Meta().Bounds
 
 	seriesMeta := seriesIter.SeriesMeta()
+
+	// rename series to exclude their __name__ tag
+	// TODO: why do we do this?
 	resultSeriesMeta := make([]block.SeriesMeta, len(seriesMeta))
 	for i, m := range seriesMeta {
 		tags := m.Tags.WithoutName()
-		resultSeriesMeta[i].Name = tags.ID()
+		resultSeriesMeta[i] = block.SeriesMeta{
+			Name: tags.ID(),
+			Tags: tags,
+		}
 	}
 
 	builder, err := c.controller.BlockBuilder(seriesIter.Meta(), resultSeriesMeta)