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>

routers/web/admin/config.go

@@ -18,8 +18,6 @@ import (
 	"gitea.dev/modules/util"
 	"gitea.dev/services/context"
 	"gitea.dev/services/mailer"
-
-	"gitea.com/go-chi/session"
 )
 
 const (
@@ -93,20 +91,6 @@ func Config(ctx *context.Context) {
 	ctx.Data["CacheItemTTL"] = setting.CacheService.TTL
 
 	sessionCfg := setting.SessionConfig
-	if sessionCfg.Provider == "VirtualSession" {
-		var realSession session.Options
-		if err := json.Unmarshal([]byte(sessionCfg.ProviderConfig), &realSession); err != nil {
-			log.Error("Unable to unmarshall session config for virtual provider config: %s\nError: %v", sessionCfg.ProviderConfig, err)
-		}
-		sessionCfg.Provider = realSession.Provider
-		sessionCfg.ProviderConfig = realSession.ProviderConfig
-		sessionCfg.CookieName = realSession.CookieName
-		sessionCfg.CookiePath = realSession.CookiePath
-		sessionCfg.Gclifetime = realSession.Gclifetime
-		sessionCfg.Maxlifetime = realSession.Maxlifetime
-		sessionCfg.Secure = realSession.Secure
-		sessionCfg.Domain = realSession.Domain
-	}
 	sessionCfg.ProviderConfig = ""
 	ctx.Data["SessionConfig"] = sessionCfg