Secrets storage with SecretKey encrypted (#22142)

Fork of #14483, but [gave up
MasterKey](https://github.com/go-gitea/gitea/pull/14483#issuecomment-1350728557),
and fixed some problems.

Close #12065.
Needed by #13539.

Featrues:
- Secrets for repo and org, not user yet.
- Use SecretKey to encrypte/encrypt secrets.
- Trim spaces of secret value.
- Add a new locale ini block, to make it easy to support secrets for
user.

Snapshots:

Repo level secrets:

![image](https://user-images.githubusercontent.com/9418365/207823319-b8a4903f-38ca-4af7-9d05-336a5af906f3.png)

Rrg level secrets

![image](https://user-images.githubusercontent.com/9418365/207823371-8bd02e93-1928-40d1-8c76-f48b255ace36.png)

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

services/forms/user_form.go

@@ -363,6 +363,18 @@ func (f *AddKeyForm) Validate(req *http.Request, errs binding.Errors) binding.Er
 	return middleware.Validate(errs, ctx.Data, f, ctx.Locale)
 }
 
+// AddSecretForm for adding secrets
+type AddSecretForm struct {
+	Title   string `binding:"Required;MaxSize(50)"`
+	Content string `binding:"Required"`
+}
+
+// Validate validates the fields
+func (f *AddSecretForm) Validate(req *http.Request, errs binding.Errors) binding.Errors {
+	ctx := context.GetContext(req)
+	return middleware.Validate(errs, ctx.Data, f, ctx.Locale)
+}
+
 // NewAccessTokenForm form for creating access token
 type NewAccessTokenForm struct {
 	Name string `binding:"Required;MaxSize(255)"`