Report operational metrics #36

Collect and report operational metrics

Candidate metrics

• tx/s
• outbox size
• confirm rates
• pending saga instances
• confirm rates
• saga timeout
• health errors

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