Delete unwanted host records in batches

Delete unwanted host records in batches

This adds a batched migration, which:

1. Finds all CurrentHostStats within the range of ids
2. that have not a single Usage Ping
3. that have been created this year

Then we start an iteration over those candidates:

1. Continue, if there exists a UsagePingError for the host
2. Get all version checks for the related host
3. continue, if a single version check is safe to keep
4. Otherwise deletes: VersionChecks, CurrentHostStats related to the host and the host itself.