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_test.go

@@ -18,16 +18,6 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestRemoveSessionCookieHeader(t *testing.T) {
-	w := httptest.NewRecorder()
-	w.Header().Add("Set-Cookie", (&http.Cookie{Name: setting.SessionConfig.CookieName, Value: "foo"}).String())
-	w.Header().Add("Set-Cookie", (&http.Cookie{Name: "other", Value: "bar"}).String())
-	assert.Len(t, w.Header().Values("Set-Cookie"), 2)
-	removeSessionCookieHeader(w)
-	assert.Len(t, w.Header().Values("Set-Cookie"), 1)
-	assert.Contains(t, "other=bar", w.Header().Get("Set-Cookie"))
-}
-
 func TestServerErrorFetchActionRespondsJSON(t *testing.T) {
 	req, _ := http.NewRequest(http.MethodPost, "/", nil)
 	req.Header.Add("X-Gitea-Fetch-Action", "1")