refactor!: move go-chi/session into Gitea (#39504)

The `gitea.com/go-chi/session` package only exists for Gitea, so it
moves into `modules/session` to fix its bugs directly. Fixes the flake
in
https://github.com/go-gitea/gitea/actions/runs/36726154500/job/109923538400.

- Sessions are only written back when changed, so a read-only request
can't revert a concurrent change or restore a logged-out session, like
https://github.com/go-macaron/session/commit/ae808a4a4660c802965c834299ab08f167effd12
- The session cookie is only set once a session holds data
- Every backend refreshes the expiry on load and file sessions are
written atomically
- Also fix  https://github.com/go-gitea/gitea/issues/36176

## ⚠️ BREAKING ⚠️

* the `mysql`, `postgres`, `couchbase` and `memcache` session providers
are removed, use `file`, `db` or `redis` instead
* login-related cookies are renamed to `gitea_session` and
`gitea_remember`, if you'd like to use the old names, set `COOKIE_NAME`
and `COOKIE_REMEMBER_NAME` in app.ini

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/context/context_cookie.go

@@ -4,26 +4,11 @@
 package context
 
 import (
-	"net/http"
-	"strings"
-
-	"gitea.dev/modules/setting"
 	"gitea.dev/modules/web/middleware"
 )
 
 const CookieNameFlash = "gitea_flash"
 
-func removeSessionCookieHeader(w http.ResponseWriter) {
-	cookies := w.Header()["Set-Cookie"]
-	w.Header().Del("Set-Cookie")
-	for _, cookie := range cookies {
-		if strings.HasPrefix(cookie, setting.SessionConfig.CookieName+"=") {
-			continue
-		}
-		w.Header().Add("Set-Cookie", cookie)
-	}
-}
-
 // SetSiteCookie convenience function to set most cookies consistently
 func (ctx *Context) SetSiteCookie(name, value string, maxAge int) {
 	middleware.SetSiteCookie(ctx.Resp, name, value, maxAge)