Add warning when using relative path to app.ini (#10104)

Co-authored-by: Lauris BH <lauris@nix.lv>

modules/setting/setting.go

@@ -511,6 +511,7 @@ func SetCustomPathAndConf(providedCustom, providedConf, providedWorkPath string)
 		CustomConf = path.Join(CustomPath, "conf/app.ini")
 	} else if !filepath.IsAbs(CustomConf) {
 		CustomConf = path.Join(CustomPath, CustomConf)
+		log.Warn("Using 'custom' directory as relative origin for configuration file: '%s'", CustomConf)
 	}
 }