Proposal: Enable a default connection logger

[philon-msft]

Currently ConnectionMultiplexer supports outputting logs from connect/reconnect operations. This is helpful for debugging connections issues, but it's difficult to discover and use this capability. Users need to create a TextWriter instance and pass it in to the .Connect() call. Can we make it easier, by turning on logging by default and exposing log output via a string property on ConnectionMultiplexer?

Design details:

• Control the default connection logger via new ConfigurationOptions field, enabled by default.
• ConnectionMultiplexer would instantiate its own TextWriter internally and write to it.
• With automatic reconnections the log could grow unbounded, so it should be a rolling log that retains only one or two most recent connections.
• If the user passes in a TextWriter via the existing .Connect() parameter, we should continue writing to that as we currently do, in addition to writing to the internal log.
• Documentation will also need to be updated to cover the simpler experience using the new default logger.