server: Prepare "GET /maintenance" endpoint

This is useful for running occasional maintenance tasks.

server/app/controllers/MaintenanceController.scala

@@ -0,0 +1,17 @@
+package controllers
+
+import controllers.common.{MyJsonController, MyJsonControllerComponents}
+import javax.inject.Inject
+import org.scalactic.Good
+import play.api.libs.json.JsObject
+
+import scala.concurrent.Future
+
+class MaintenanceController @Inject() (
+    components: MyJsonControllerComponents)
+    extends MyJsonController(components) {
+
+  def run() = public { _ =>
+    Future.successful(Good(JsObject.empty))
+  }
+}

server/conf/routes

@@ -4,6 +4,7 @@
 # ~~~~
 
 GET   /health                controllers.HealthController.check()
+# GET   /maintenance           controllers.MaintenanceController.run()
 
 GET   /transactions/:txid        controllers.TransactionsController.getTransaction(txid: String)
 GET   /transactions/:txid/raw    controllers.TransactionsController.getRawTransaction(txid: String)