Support configuration variables on Gitea Actions (#24724)

Co-Author: @silverwind @wxiaoguang 
Replace: #24404

See:
- [defining configuration variables for multiple
workflows](https://docs.github.com/en/actions/learn-github-actions/variables#defining-configuration-variables-for-multiple-workflows)
- [vars
context](https://docs.github.com/en/actions/learn-github-actions/contexts#vars-context)

Related to:
- [x] protocol: https://gitea.com/gitea/actions-proto-def/pulls/7
- [x] act_runner: https://gitea.com/gitea/act_runner/pulls/157
- [x] act: https://gitea.com/gitea/act/pulls/43

#### Screenshoot
Create Variable:

![image](https://user-images.githubusercontent.com/33891828/236758288-032b7f64-44e7-48ea-b07d-de8b8b0e3729.png)


![image](https://user-images.githubusercontent.com/33891828/236758174-5203f64c-1d0e-4737-a5b0-62061dee86f8.png)

Workflow:
```yaml
  test_vars:
    runs-on: ubuntu-latest
    steps:
      - name: Print Custom Variables
        run: echo "${{ vars.test_key }}"
      - name: Try to print a non-exist var
        run: echo "${{ vars.NON_EXIST_VAR }}"
```

Actions Log:

![image](https://user-images.githubusercontent.com/33891828/236759075-af0c5950-368d-4758-a8ac-47a96e43b6e2.png)

---
This PR just implement the org / user (depends on the owner of the
current repository) and repo level variables, The Environment level
variables have not been implemented.
Because
[Environment](https://docs.github.com/en/actions/deployment/targeting-different-environments/using-environments-for-deployment#about-environments)
is a module separate from `Actions`. Maybe it would be better to create
a new PR to do it.

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

routers/web/repo/setting/variables.go

@@ -0,0 +1,119 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import (
+	"errors"
+	"net/http"
+
+	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/setting"
+	shared "code.gitea.io/gitea/routers/web/shared/actions"
+)
+
+const (
+	tplRepoVariables base.TplName = "repo/settings/actions"
+	tplOrgVariables  base.TplName = "org/settings/actions"
+	tplUserVariables base.TplName = "user/settings/actions"
+)
+
+type variablesCtx struct {
+	OwnerID           int64
+	RepoID            int64
+	IsRepo            bool
+	IsOrg             bool
+	IsUser            bool
+	VariablesTemplate base.TplName
+	RedirectLink      string
+}
+
+func getVariablesCtx(ctx *context.Context) (*variablesCtx, error) {
+	if ctx.Data["PageIsRepoSettings"] == true {
+		return &variablesCtx{
+			RepoID:            ctx.Repo.Repository.ID,
+			IsRepo:            true,
+			VariablesTemplate: tplRepoVariables,
+			RedirectLink:      ctx.Repo.RepoLink + "/settings/actions/variables",
+		}, nil
+	}
+
+	if ctx.Data["PageIsOrgSettings"] == true {
+		return &variablesCtx{
+			OwnerID:           ctx.ContextUser.ID,
+			IsOrg:             true,
+			VariablesTemplate: tplOrgVariables,
+			RedirectLink:      ctx.Org.OrgLink + "/settings/actions/variables",
+		}, nil
+	}
+
+	if ctx.Data["PageIsUserSettings"] == true {
+		return &variablesCtx{
+			OwnerID:           ctx.Doer.ID,
+			IsUser:            true,
+			VariablesTemplate: tplUserVariables,
+			RedirectLink:      setting.AppSubURL + "/user/settings/actions/variables",
+		}, nil
+	}
+
+	return nil, errors.New("unable to set Variables context")
+}
+
+func Variables(ctx *context.Context) {
+	ctx.Data["Title"] = ctx.Tr("actions.variables")
+	ctx.Data["PageType"] = "variables"
+	ctx.Data["PageIsSharedSettingsVariables"] = true
+
+	vCtx, err := getVariablesCtx(ctx)
+	if err != nil {
+		ctx.ServerError("getVariablesCtx", err)
+		return
+	}
+
+	shared.SetVariablesContext(ctx, vCtx.OwnerID, vCtx.RepoID)
+	if ctx.Written() {
+		return
+	}
+
+	ctx.HTML(http.StatusOK, vCtx.VariablesTemplate)
+}
+
+func VariableCreate(ctx *context.Context) {
+	vCtx, err := getVariablesCtx(ctx)
+	if err != nil {
+		ctx.ServerError("getVariablesCtx", err)
+		return
+	}
+
+	if ctx.HasError() { // form binding validation error
+		ctx.JSONError(ctx.GetErrMsg())
+		return
+	}
+
+	shared.CreateVariable(ctx, vCtx.OwnerID, vCtx.RepoID, vCtx.RedirectLink)
+}
+
+func VariableUpdate(ctx *context.Context) {
+	vCtx, err := getVariablesCtx(ctx)
+	if err != nil {
+		ctx.ServerError("getVariablesCtx", err)
+		return
+	}
+
+	if ctx.HasError() { // form binding validation error
+		ctx.JSONError(ctx.GetErrMsg())
+		return
+	}
+
+	shared.UpdateVariable(ctx, vCtx.RedirectLink)
+}
+
+func VariableDelete(ctx *context.Context) {
+	vCtx, err := getVariablesCtx(ctx)
+	if err != nil {
+		ctx.ServerError("getVariablesCtx", err)
+		return
+	}
+	shared.DeleteVariable(ctx, vCtx.RedirectLink)
+}