Refactor request context (#32956)

Introduce RequestContext: is a short-lived context that is used to store
request-specific data.

RequestContext could be used to clean form tmp files, close context git
repo, and do some tracing in the future.

Then a lot of legacy code could be removed or improved. For example:
most `ctx.Repo.GitRepo.Close()` could be removed because the git repo
could be closed when the request is done.

services/auth/oauth2_test.go

@@ -9,7 +9,7 @@ import (
 
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
-	"code.gitea.io/gitea/modules/web/middleware"
+	"code.gitea.io/gitea/modules/reqctx"
 	"code.gitea.io/gitea/services/actions"
 
 	"github.com/stretchr/testify/assert"
@@ -23,7 +23,7 @@ func TestUserIDFromToken(t *testing.T) {
 		token, err := actions.CreateAuthorizationToken(RunningTaskID, 1, 2)
 		assert.NoError(t, err)
 
-		ds := make(middleware.ContextData)
+		ds := make(reqctx.ContextData)
 
 		o := OAuth2{}
 		uid := o.userIDFromToken(context.Background(), token, ds)