ISSUE
-----
`$http_host` is used for setting header 'X-Frappe-Site-Name'
which adds port number to the header along with the host value. Frappe source app.py expects the header
value to contain only the host name and not the port number. So `$host` should be used instead of
`$http_host` to set the 'X-Frappe-Site-Name' header
`$http_host` vs `$host` in nginx
--------------------------------
`$http_host` contains the host name along with port number whereas `$host` contains only the host name in lowercase without the port number.
> `$host` - This variable is equal to line Host in the header of request or
> name of the server processing the request if the Host header is not available.
> This variable may have a different value from $http_host in such cases:
> * when the Host input header is absent or has an empty value,
> `$host` equals to the value of server_name directive;
> * when the value of Host contains port number, `$host` doesn't include
> that port number. $host's value is always lowercase since 0.8.17.
> - [$host vs $http_host stackoverflow](https://stackoverflow.com/questions/15414810/whats-the-difference-of-host-and-http-host-in-nginx)
From the frappe source file [app.py](https://github.com/frappe/frappe/blob/develop/frappe/app.py#L107), X-Frappe-Site-Name is used if its set.
```Python
site = _site or request.headers.get('X-Frappe-Site-Name') or get_site_name(request.host)
```
Since `$host` variable will never contain port number which is not the case with `$http_host`,
`$host` should be used for setting the header 'X-Frappe-Site-Name'. Otherwise we have issues with site serving.
Tested the above changes in compose as well as in swarm environment.
In compose, tested the site with host mapping of 80 and 8000. Works with both the host port mapping.
Tested with erpnext version - v12.5.2
Changes to be committed:
modified: build/common/nginx-default.conf.template
