Move some files under repo/setting (#25585)

There are too many files under `routers/web/repo` and the file
`routers/web/repo/setting.go` is too big.
This PR move all setting related routers' body functions under
`routers/web/repo/setting` and also split `routers/web/repo/setting.go`

routers/web/repo/setting/main_test.go

@@ -0,0 +1,17 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import (
+	"path/filepath"
+	"testing"
+
+	"code.gitea.io/gitea/models/unittest"
+)
+
+func TestMain(m *testing.M) {
+	unittest.MainTest(m, &unittest.TestOptions{
+		GiteaRootPath: filepath.Join("..", "..", "..", ".."),
+	})
+}