Eventsourcing-helpers

Minor:
- Update dependencies

Minor:
- Add new assert method for the message bus mock backend to help validate if multiple messages were produced (74)

Minor:
- Add feature toggle for Datadog metrics (65)

Fixes
- Fix broken test (`test_add_one_consumer_message_should_be_added_to_internal_queue`)

Minor:
- Bump `confluent_kafka_helpers` verison to `0.7.7` and remove pinned versions (64)

Minor:
- Bump `confluent_kafka_helpers` verison to `0.7.6`

Fixes:
- Assert headers in Kafka messagebus mock backend (https://github.com/fyndiq/eventsourcing_helpers/pull/63)