Context:
When we read private/user reports we currently often read all reports and then filter by collectionId = null and userId. We should rather filter directly when querying from elasticsearch.
AT:
- ReportReader offers a method to filter for private reports with an optional userId
- in every location where we read private reports this method is used, these are at least:
- `ReportService#findAndFilterPrivateReports`
- `#UpgradeFrom26To27#populateReportToAlertArchiveCollectionMap`