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>

docs/content/doc/secrets/overview.en-us.md

@@ -0,0 +1,36 @@
+---
+date: "2022-12-19T21:26:00+08:00"
+title: "Encrypted secrets"
+slug: "secrets/overview"
+draft: false
+toc: false
+menu:
+  sidebar:
+    parent: "secrets"
+    name: "Overview"
+    weight: 1
+    identifier: "overview"
+---
+
+# Encrypted secrets
+
+Encrypted secrets allow you to store sensitive information in your organization or repository.
+Secrets are available on Gitea 1.19+.
+
+# Naming your secrets
+
+The following rules apply to secret names:
+
+Secret names can only contain alphanumeric characters (`[a-z]`, `[A-Z]`, `[0-9]`) or underscores (`_`). Spaces are not allowed.
+
+Secret names must not start with the `GITHUB_` and `GITEA_` prefix.
+
+Secret names must not start with a number.
+
+Secret names are not case-sensitive.
+
+Secret names must be unique at the level they are created at.
+
+For example, a secret created at the repository level must have a unique name in that repository, and a secret created at the organization level must have a unique name at that level.
+
+If a secret with the same name exists at multiple levels, the secret at the lowest level takes precedence. For example, if an organization-level secret has the same name as a repository-level secret, then the repository-level secret takes precedence.