This adds instrumentation for the number of bytes written to and read
from Redis. To avoid having to monkey-patch multiple methods of
Redis::Client, this change introduces a custom Redis driver which
inherits from the default Redis::Connection::Ruby driver.

Counts include the size of the commands (GET, SET etc.), but exclude
the size overhead of Redis serialization (type, length prefix,
trailing \r\n).

https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/318