Update usage ping data to track MRs with added rules

Problem to solve

Related to #220541 (closed)

We need to answer the question: How many MRS have added rules specific to the merge request?

Proposal

From #220541 (comment 358825262):

We can get this by querying the approval_merge_request_rules table and joining it with approval_merge_request_rule_sources table. Determine which of approval_merge_request_rules records have no approval_merge_request_rule_sources. Then do a distinct count by merge_request_id.