Fix all possible setting error related storages and added some tests (#23911)

Follow up #22405

Fix #20703 

This PR rewrites storage configuration read sequences with some breaks
and tests. It becomes more strict than before and also fixed some
inherit problems.

- Move storage's MinioConfig struct into setting, so after the
configuration loading, the values will be stored into the struct but not
still on some section.
- All storages configurations should be stored on one section,
configuration items cannot be overrided by multiple sections. The
prioioty of configuration is `[attachment]` > `[storage.attachments]` |
`[storage.customized]` > `[storage]` > `default`
- For extra override configuration items, currently are `SERVE_DIRECT`,
`MINIO_BASE_PATH`, `MINIO_BUCKET`, which could be configured in another
section. The prioioty of the override configuration is `[attachment]` >
`[storage.attachments]` > `default`.
- Add more tests for storages configurations.
- Update the storage documentations.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

tests/test_utils.go

@@ -214,7 +214,9 @@ func PrepareTestEnv(t testing.TB, skip ...int) func() {
 
 	// load LFS object fixtures
 	// (LFS storage can be on any of several backends, including remote servers, so we init it with the storage API)
-	lfsFixtures, err := storage.NewStorage("", storage.LocalStorageConfig{Path: path.Join(filepath.Dir(setting.AppPath), "tests/gitea-lfs-meta")})
+	lfsFixtures, err := storage.NewStorage(setting.LocalStorageType, &setting.Storage{
+		Path: filepath.Join(filepath.Dir(setting.AppPath), "tests/gitea-lfs-meta"),
+	})
 	assert.NoError(t, err)
 	assert.NoError(t, storage.Clean(storage.LFS))
 	assert.NoError(t, lfsFixtures.IterateObjects("", func(path string, _ storage.Object) error {