v2.6.0

• [Improvement] Introduce client_class setting for ability to replace underlying client with anything specific to a given env (dev, test, etc).
• [Improvement] Introduce Clients::Buffered useful for writing specs that do not have to talk with Kafka (id-ilych)
• [Improvement] Make #produce method private to avoid confusion and make sure it is not used directly (it is not part of the official API).
• [Change] Change wait_on_queue_full from false to true as a default.
• [Change] Rename wait_on_queue_full_timeout to wait_backoff_on_queue_full to match what it actually does.
• [Enhancement] Introduce wait_timeout_on_queue_full with proper meaning. That is, this represents time after which despite backoff the error will be raised. This should allow to raise an error in case the backoff attempts were insufficient. This prevents from a case, where upon never deliverable messages we would end up with an infinite loop.
• [Fix] Provide type for queue full errors that references the appropriate public API method correctly.