PoC: pages without wildcard domain

We want to allow users to run pages without wildcard SSL/DNS

One of the ideas is to put namespace into the first path segment.

This MR adds middleware which puts the first path segment back into host before handling the request.

It works for me:

Not addressed topics

• Auth

• SSL

• Lets Encrypt's SSL

• Anything involving redirects

  The idea is to provide custom http.ResponseWriter which will proxy every method to original ResponseWriter, but will override WriteHeaders and change the value of Location header before sending.

Related issues

• gitlab#29841 (closed)
• gitlab#17584 (closed)