Add Cache-Control header to html and api responses, add no-transform (#20432)

`no-transform` allegedly disables CloudFlare auto-minify and we did not
set caching headers on html or api requests, which seems good to have
regardless.

Transformation is still allowed for asset requests.

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Andrew Thornton <art27@cantab.net>

routers/install/routes.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"path"
 
+	"code.gitea.io/gitea/modules/httpcache"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/public"
 	"code.gitea.io/gitea/modules/setting"
@@ -62,6 +63,7 @@ func installRecovery() func(next http.Handler) http.Handler {
 						"SignedUserName": "",
 					}
 
+					httpcache.AddCacheControlToHeader(w.Header(), 0, "no-transform")
 					w.Header().Set(`X-Frame-Options`, setting.CORSConfig.XFrameOptions)
 
 					if !setting.IsProd {