Upgrade to brod 3.3.4 (#37)

Also includes minor fixes:
- Correct brod roundrobin (v1) protocol commits by `+1`
- Lagging is committed_offset - hw_offset without extra -1
- Sort topic-partition in consumer group offset display GUI
- Avoid enumerating brod's dependency in mix.exs

Add missing newline at the end of the metrics export (#34)

* Add missing newline at the end of the metrics export

* Add docker compose for kastlex + kafka + prometheus

In order to ease manual testing of kastlex <=> prometheus integration

Fix topic offset format string (#33)

Fix topic offset format string

Missing comma

Expose /metrics endpoint in Prometheus format (#31)

* Expose /metrics endpoint in Prometheus format

Only text format is available. No client library is used, as they assume constant set of metrics
instead of the dynamic list we generate based on kafka topics and consumer groups.

* Make /metrics code more idiomatic

* Add manual testing instructions

* Split topic and consumer group offset export

Add method to get all recorded topic offsets.

* Use simpler map syntax

* Add header version. Add basic tests

* Version bump

* Add metric types

Merge pull request #26 from klarna/update-to-brod-3.0

Update to brod 3.0

Ensure brod_consumer running before trying to re-subscribe (#27)

fix accept headers

fix environment variables processing

update dependencies

fix tests and support application/binary (#24)

fixes #12
fixes #13
fixes #22
fixes #23