Some server log messages are not logged to Logback

Nobody has claimed this yet.

I found this from the stderr output:

```
Aug 06, 2019 3:18:22 PM com.github.benmanes.caffeine.cache.LocalAsyncCache lambda$handleCompletion$3
WARNING: Exception thrown during asynchronous load
java.util.concurrent.CompletionException: com.linecorp.centraldogma.server.internal.storage.RequestAlreadyTimedOutException: Request already timed out.
at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:314)
at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)
at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1702)
at io.micrometer.core.instrument.AbstractTimer.record(AbstractTimer.java:160)
at io.micrometer.core.instrument.Timer.lambda$wrap$0(Timer.java:144)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: com.linecorp.centraldogma.server.internal.storage.RequestAlreadyTimedOutException: Request already timed out.
```

Start by tracing the stderr output from com.github.benmanes.caffeine.cache.LocalAsyncCache and the asynchronous load that reports RequestAlreadyTimedOutException. Identify the server logging entry points involved and verify that the affected messages are routed through Logback rather than only appearing on stderr.

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