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>

templates/admin/repo/unadopted.tmpl

@@ -32,7 +32,6 @@
 											<p>{{ctx.Locale.Tr "repo.adopt_preexisting_content" $dir}}</p>
 										</div>
 										<form class="ui form" method="post" action="{{AppSubUrl}}/-/admin/repos/unadopted">
-											{{$.CsrfTokenHtml}}
 											<input type="hidden" name="id" value="{{$dir}}">
 											<input type="hidden" name="action" value="adopt">
 											<input type="hidden" name="q" value="{{$.Keyword}}">
@@ -49,7 +48,6 @@
 											<p>{{ctx.Locale.Tr "repo.delete_preexisting_content" $dir}}</p>
 										</div>
 										<form class="ui form" method="post" action="{{AppSubUrl}}/-/admin/repos/unadopted">
-											{{$.CsrfTokenHtml}}
 											<input type="hidden" name="id" value="{{$dir}}">
 											<input type="hidden" name="action" value="delete">
 											<input type="hidden" name="q" value="{{$.Keyword}}">