add logback layout for structured JSON logging (#4184)

delta/app/src/main/scala/ch/epfl/bluebrain/nexus/delta/logback/JsonLayout.scala

@@ -0,0 +1,22 @@
+package ch.epfl.bluebrain.nexus.delta.logback
+
+import ch.qos.logback.classic.spi.{ILoggingEvent, ThrowableProxyUtil}
+import ch.qos.logback.core.LayoutBase
+import io.circe.Json
+import io.circe.syntax._
+
+class JsonLayout extends LayoutBase[ILoggingEvent] {
+  override def doLayout(event: ILoggingEvent): String = {
+    val stackTraceField = Option(event.getThrowableProxy).map("stackTrace" := ThrowableProxyUtil.asString(_))
+    Json
+      .fromFields(
+        Map(
+          "message" := event.getMessage,
+          "level"   := event.getLevel.toString,
+          "time"    := event.getInstant,
+          "logger"  := event.getLoggerName
+        ) ++ stackTraceField
+      )
+      .noSpaces + '\n'
+  }
+}