Allow to configure a region for s3 backend

Closes: #2386

modules/joex/src/main/resources/reference.conf

@@ -739,6 +739,7 @@ Docpell Update Check
          access-key = "username"
          secret-key = "password"
          bucket = "docspell"
+         region = ""
        }
     }
   }

modules/joex/src/main/scala/docspell/joex/ConfigFile.scala

@@ -60,7 +60,7 @@ object ConfigFile {
         cfg => cfg.updateCheck.enabled && cfg.updateCheck.subject.els.isEmpty,
         "No subject given for enabled update check!"
       ),
-      Validation(cfg => cfg.files.validate.map(_ => cfg)),
+      Validation(cfg => cfg.files.validate.map(f => cfg.copy(files = f))),
       Validation.failWhen(
         cfg =>
           cfg.fullTextSearch.enabled &&