add logback layout for structured JSON logging

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

@@ -0,0 +1,20 @@
+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'
+  }
+}