Make the logging of server connections configurable

[roccodev]

Makes the logging of server connections ([server connection] Player -> SERVER has (dis)connected) configurable.

I think MinecraftConnection can only handle VelocityServerConnections, but I added an instance check anyway.

[A248]

Any and all log messages in Velocity are already configurable via log4j2. I'd suggest you refer to such documentation on logging. It's quite powerful.

[roccodev]

While that's a good thing, log messages for command invocations are already configurable, and I wouldn't expect most server owners to be familiar with log4j. If this ends up being added I would move all the logging-related settings to a logging section in the config.

[4drian3d]

Since pull request #673 was merged, I think this pull request can be closed

[4drian3d]

This change was already integrated in pull request #673 (2 years ago)