DEBUG ERRORS

[talbii]

Closes #1531.

Logs errors in a Redis connection to an additional sink buffer, and returns them whenever DEBUG ERRORS is invoked. The sink buffer is stored within RedisReplyBuilder, and is given in the constructor. It is individual per ReplyBuilder, hence per connection.

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very MVP for now, no need to review unless you see something critical :)

• Log input string (the invoked command, CID) as well
  • $\star$ Log full input string (CID + arguments)
• Replace StringSink with a RingBufferSink RingBuffer<std::string>
• Tidy up

[talbii]

@romange Hey! What's the status of this PR? When I left it was ready for review. Happy to do any corrections as needed 😄