outbox_total_records: reports the total amount of records currently in the outbox
outbox_pending_delivery: reports the total amount of records pending delivery currently in the outbox
outbox_pending_removal: reports the total amount of records that were sent and pending removal currently in the outbox
Transactional Outbox Metrics:
outbox_total_records: reports the total amount of records currently in the outbox outbox_pending_delivery: reports the total amount of records pending delivery currently in the outbox outbox_pending_removal: reports the total amount of records that were sent and pending removal currently in the outbox
related issue: #36