add a new internal hook to save ssh log (#15787)

* add a new internal hook to save ssh log

as title, when a ssh error ocure like #15785.
only when switch ``RUN_MODE`` to dev can we
found which error is ocure. But this way is
not a good idea for production envirment.

this changes try save ssh error mesage to the
log file like other log by a new internal hook.
I think it's usefull for find error message
in production envirment. Thanks.

Signed-off-by: a1012112796 <1012112796@qq.com>

* rename and fix nit

* Update modules/private/hook.go

Co-authored-by: silverwind <me@silverwind.io>

Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -657,6 +657,7 @@ Default templates for project boards:
 - `ROUTER`: **console**: The mode or name of the log the router should log to. (If you set this to `,` it will log to default gitea logger.)
 NB: You must have `DISABLE_ROUTER_LOG` set to `false` for this option to take effect. Configure each mode in per mode log subsections `\[log.modename.router\]`.
 - `ENABLE_ACCESS_LOG`: **false**: Creates an access.log in NCSA common log format, or as per the following template
+- `ENABLE_SSH_LOG`: **false**: save ssh log to log file
 - `ACCESS`: **file**: Logging mode for the access logger, use a comma to separate values. Configure each mode in per mode log subsections `\[log.modename.access\]`. By default the file mode will log to `$ROOT_PATH/access.log`. (If you set this to `,` it will log to the default gitea logger.)
 - `ACCESS_LOG_TEMPLATE`: **`{{.Ctx.RemoteAddr}} - {{.Identity}} {{.Start.Format "[02/Jan/2006:15:04:05 -0700]" }} "{{.Ctx.Req.Method}} {{.Ctx.Req.URL.RequestURI}} {{.Ctx.Req.Proto}}" {{.ResponseWriter.Status}} {{.ResponseWriter.Size}} "{{.Ctx.Req.Referer}}\" \"{{.Ctx.Req.UserAgent}}"`**: Sets the template used to create the access log.
   - The following variables are available: