Sub directory based url for Pages

ZD: https://gitlab.zendesk.com/agent/tickets/32665

Description

Had a call with a customer on the gov sector and he made an excellent point about them not being able to generate wildcard certificates for their custom domain pages requirement. This might be the case for this sector in general.

Also related: https://gitlab.com/gitlab-org/gitlab-pages/issues/5

@ayufan do we have any thoughts or workarounds ?