Backport #26999
If the AppURL(ROOT_URL) is an HTTPS URL, then the COOKIE_SECURE's
default value should be true.
And, if a user visits an "http" site with "https" AppURL, they won't be
able to login, and they should have been warned. The only problem is
that the "language" can't be set either in such case, while I think it
is not a serious problem, and it could be fixed easily if needed.
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
