Baseplate

Fixes
* Fix accessing non-existent Span object by zerozez in https://github.com/reddit/baseplate.py/pull/754
* Reduce cardinality of http_server_active_requests by SuperQ in https://github.com/reddit/baseplate.py/pull/745

New Contributors
* zerozez made their first contribution in https://github.com/reddit/baseplate.py/pull/754

**Full Changelog**: https://github.com/reddit/baseplate.py/compare/v2.5.7...v2.5.8-beta.4

What's Changed
* exposing prometheus metrics from event-publisher sidecar by ghirsch-reddit in https://github.com/reddit/baseplate.py/pull/742
* upgrade flake8 and pylint by ghirsch-reddit in https://github.com/reddit/baseplate.py/pull/750
* BASEPLATE_SIDECAR_(s/METRICS/ADMIN)_PORT by ghirsch-reddit in https://github.com/reddit/baseplate.py/pull/749
* test(RedisClient): Use common setup/teardown logic in tests by KTAtkinson in https://github.com/reddit/baseplate.py/pull/744
* fix(runtime metrics): Use a null statsd client for runtime metrics by KTAtkinson in https://github.com/reddit/baseplate.py/pull/751
* Revert "exposing prometheus metrics from event-publisher sidecar (742)" by ghirsch-reddit in https://github.com/reddit/baseplate.py/pull/753

New Contributors
* ghirsch-reddit made their first contribution in https://github.com/reddit/baseplate.py/pull/742

**Full Changelog**: https://github.com/reddit/baseplate.py/compare/v2.5.6...v2.5.7