Refactor the setting to make unit test easier (#22405)

Some bugs caused by less unit tests in fundamental packages. This PR
refactor `setting` package so that create a unit test will be easier
than before.

- All `LoadFromXXX` files has been splited as two functions, one is
`InitProviderFromXXX` and `LoadCommonSettings`. The first functions will
only include the code to create or new a ini file. The second function
will load common settings.
- It also renames all functions in setting from `newXXXService` to
`loadXXXSetting` or `loadXXXFrom` to make the function name less
confusing.
- Move `XORMLog` to `SQLLog` because it's a better name for that.

Maybe we should finally move these `loadXXXSetting` into the `XXXInit`
function? Any idea?

---------

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: delvh <dev.lh@web.de>

modules/setting/metrics.go

@@ -0,0 +1,21 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+// Metrics settings
+var Metrics = struct {
+	Enabled                  bool
+	Token                    string
+	EnabledIssueByLabel      bool
+	EnabledIssueByRepository bool
+}{
+	Enabled:                  false,
+	Token:                    "",
+	EnabledIssueByLabel:      false,
+	EnabledIssueByRepository: false,
+}
+
+func loadMetricsFrom(rootCfg ConfigProvider) {
+	mustMapSetting(rootCfg, "metrics", &Metrics)
+}