Silences: Optimize incremental mutes queries via a silence version index (#4723)

* Add silence version index an QSince query

Signed-off-by: Guido Trotter <[email protected]>

* Add scanned total, skipped total, and indices/state sizes metrics

Signed-off-by: Guido Trotter <[email protected]>

* Use QSince to optimize Mutes: we can now only scan old silences, and new silences that have been added since the last version we saw

Signed-off-by: Guido Trotter <[email protected]>

* query: pre-guess the allocation result size

Signed-off-by: Guido Trotter <[email protected]>

* Rename versionIndex.find to versionIndex.findVersionGreaterThan

Signed-off-by: Guido Trotter <[email protected]>

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Signed-off-by: Guido Trotter <[email protected]>
Co-authored-by: Guido Trotter <[email protected]>

Author: ultrotter