staging: Update graphql vhost

the vhost is set by apache to the host it calls (ProxyPreserveHost is set to false for all the apache configurations)

Related to swh/infra/sysadm-environment#4603 (closed)

tested locally with a temporary ingress:

http --verify=no --headers https://webapp.staging.swh.network/graphql/
HTTP/1.1 200 OK
Accept-Ranges: bytes
Age: 23
Connection: keep-alive
Content-Encoding: gzip
Content-Length: 703
Content-Type: text/html; charset=utf-8
Date: Wed, 18 Jan 2023 16:12:48 GMT
Server: Apache
Strict-Transport-Security: max-age=15768000;
Vary: Accept-Encoding
Via: 1.1 webapp.staging.swh.network
Via: 1.1 varnish (Varnish/6.5)
X-Varnish: 22 163852

It must be merged after the redirect in puppet is landed

/cc @teams/sysadmin