chore: optionally prefix authentication related cookies (#22148)

When the deployment option is enabled auth cookies are prefixed with
`__HOST-`
([info](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Set-Cookie)).

This is all done in a middleware that intercepts all requests and strips
the prefix on incoming request cookies.

coderd/userauth.go

@@ -704,7 +704,7 @@ func (api *API) postLogout(rw http.ResponseWriter, r *http.Request) {
 		Name:   codersdk.SessionTokenCookie,
 		Path:   "/",
 	}
-	http.SetCookie(rw, cookie)
+	http.SetCookie(rw, api.DeploymentValues.HTTPCookies.Apply(cookie))
 
 	// Delete the session token from database.
 	apiKey := httpmw.APIKey(r)