This adds a parameter to the storage selection interface which allows
query engine(s) to pass information about the operations surrounding a
data selection.
This can for example be used by remote storage backends to infer the
correct downsampling aggregates that need to be provided.
* Fast path the merge querier such that it is completely removed from query path when there is no remote storage.
* Add NoopQuerier
* Add copyright notice.
* Avoid global, use a function.