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>

custom/conf/app.example.ini

@@ -459,7 +459,7 @@ INTERNAL_TOKEN =
 ;LOGIN_REMEMBER_DAYS = 31
 ;;
 ;; Name of cookie used to store authentication information.
-;COOKIE_REMEMBER_NAME = gitea_incredible
+;COOKIE_REMEMBER_NAME = gitea_remember
 ;;
 ;; URL or path that Gitea should redirect users to *after* performing its own logout.
 ;; Use this, if needed, when authentication is handled by a reverse proxy or SSO.
@@ -2012,19 +2012,17 @@ LEVEL = Info
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;
-;; Either "memory", "file", "redis", "db", "mysql", "couchbase", "memcache" or "postgres"
-;; Default is "file". "db" will reuse the configuration in [database]
+;; Either "memory", "file", "redis" or "db", default is "file". "db" will reuse the configuration in [database]
 ;PROVIDER = file
 ;;
 ;; Provider config options
 ;; memory: doesn't have any config yet
 ;; file: session file path, e.g. `data/sessions`, relative paths will be made absolute against _`AppWorkPath`_.
 ;; redis: default to [redis] CONN_STR
-;; mysql: go-sql-driver/mysql dsn config string, e.g. `root:password@/session_table`
 ;PROVIDER_CONFIG =
 ;;
 ;; Session cookie name
-;COOKIE_NAME = i_like_gitea
+;COOKIE_NAME = gitea_session
 ;;
 ;; If you use session in https only: true or false. If not set, it defaults to `true` if the ROOT_URL is an HTTPS URL.
 ;COOKIE_SECURE =