Given the implicit convention that an egress bridge containing the
`local_topic` config will forward messages without the need for a rule
action, this was added to avoid needing a rule action.
- MQTT topic should be a binary
- use correct gauge functions from `wolff_metrics`.
- don't double increment success counter for kafka action
- adds a few more metrics assertions
This commit adds support for counters and gauges to the Kafka Brige.
The Kafka bridge uses [Wolff](https://github.com/kafka4beam/wolff) for
the Kafka connection. Wolff does its own batching and does not use the
batching functionality in `emqx_resource_worker` that is used by other
bridge types. Therefore, the counter events have to be generated by
Wolff. We have added
[telemetry](https://github.com/beam-telemetry/telemetry) events to Wolff
that we hook into to change counters and gauges for the Kafka bridge. The
counter called `matched` does not depend on specific functionality of
any bridge type so the updates of this counter is moved higher up in the
call chain then previously so that it also gets updated for Kafka
bridges.
Zaiming (Stone) Shi