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>

cmd/dump.go

@@ -353,9 +353,9 @@ func runDump(ctx *cli.Context) error {
 		}
 
 		excludes = append(excludes, setting.RepoRootPath)
-		excludes = append(excludes, setting.LFS.Path)
-		excludes = append(excludes, setting.Attachment.Path)
-		excludes = append(excludes, setting.Packages.Path)
+		excludes = append(excludes, setting.LFS.Storage.Path)
+		excludes = append(excludes, setting.Attachment.Storage.Path)
+		excludes = append(excludes, setting.Packages.Storage.Path)
 		excludes = append(excludes, setting.Log.RootPath)
 		excludes = append(excludes, absFileName)
 		if err := addRecursiveExclude(w, "data", setting.AppDataPath, excludes, verbose); err != nil {