Backport #26883
This change was caused by #26271, for configuration as below:
```
[attachment]
ENABLE = true
PATH = data/attachments
MAX_SIZE = 100
MAX_FILES = 5
```
Before #26271, the resolved path is ${AppWorkPath}/${attachments.PATH}
(such as `/var/lib/gitea/data/attachments`)
After #26271, the resolved path is ${AppDataPath}/${attachments.PATH}
(such as `/var/lib/gitea/data/data/attachments`)
Fix https://github.com/go-gitea/gitea/issues/26864 Follow
https://github.com/go-gitea/gitea/pull/26271
Backport #26267 by @wxiaoguang
1. Fix the wrong document (add the missing `MODE=`)
2. Add a more friendly log message to tell users to add `MODE=` in their
config
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Backport #26068 by @felixvictor
The setting `MAILER_TYPE` is deprecated.
According to the config cheat sheet, it should be `PROTOCOL`.
Co-authored-by: Felix Victor <felix.victor.na@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
