Replace CSRF cookie with CrossOriginProtection (#36183)

Removes the CSRF cookie in favor of
[`CrossOriginProtection`](https://pkg.go.dev/net/http#CrossOriginProtection)
which relies purely on HTTP headers.

Fixes: https://github.com/go-gitea/gitea/issues/11188
Fixes: https://github.com/go-gitea/gitea/issues/30333
Helps: https://github.com/go-gitea/gitea/issues/35107

TODOs:

- [x] Fix tests
- [ ] Ideally add tests to validates the protection

---------

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

tests/integration/repo_migrate_test.go

@@ -27,7 +27,6 @@ func testRepoMigrate(t testing.TB, session *TestSession, cloneAddr, repoName str
 	assert.True(t, exists, "The template has changed")
 
 	req = NewRequestWithValues(t, "POST", link, map[string]string{
-		"_csrf":      htmlDoc.GetCSRF(),
 		"clone_addr": cloneAddr,
 		"uid":        uid,
 		"repo_name":  repoName,