[Task]: Consider re-adding the `.has_matches` statsd ping for scanners

[willdurand]

Description

The scanner webhooks don't send the .has_matches ping right now. The question is whether we should add such a ping? (taking into consideration that we have async scanners nowadays).

Acceptance Criteria

see above

┆Issue is synchronized with this Jira Task

[willdurand]

same question for the individual (matching) rules