airframe-http: Add a method for storing server exceptions: TLS_KEY_SERVER_EXCEPTION (#1351)

* Add setThreadLocal method for the pre-defined key TLS_KEY_SERVER_EXCEPTION

* Update HttpBackend.scala

Co-authored-by: Taro L. Saito <leo@xerial.org>

Author: shimamoto

airframe-http/src/main/scala/wvlet/airframe/http/HttpBackend.scala

@@ -65,6 +65,9 @@ trait HttpBackend[Req, Resp, F[_]] { self =>
   // Prepare a thread-local holder for passing parameter values
   def withThreadLocalStore(request: => F[Resp]): F[Resp]
 
+  // Set a thread-local context parameter value for a pre-defined key
+  def setThreadLocalServerException[A](value: A): Unit = setThreadLocal(HttpBackend.TLS_KEY_SERVER_EXCEPTION, value)
+
   // Set a thread-local context parameter value
   def setThreadLocal[A](key: String, value: A): Unit