add etesync template (#64)

@muppeth I don't manage to add frontend to for example https://etesync.example.org/web

I tried to add something like:

```
location /web {
        alias /var/www/etesync-web/;
        index index.html;
}

```

But the static files give error 404.

Also, at the moment, access to https://etesync.example.org gives that generic page:
```
It works!

Please refer to the README to complete the final steps if you haven't done so already.
```

I don't know how to properly remove that by etesync-web

Reviewed-on: #64
Reviewed-by: muppeth <muppeth@no-reply@disroot.org>
Co-authored-by: meaz <meaz@no-reply@disroot.org>
Co-committed-by: meaz <meaz@no-reply@disroot.org>

templates/etc/nginx/sites-available/etesync.j2

@@ -0,0 +1,35 @@
+# the upstream component nginx needs to connect to
+upstream etebase {
+    server unix:///tmp/etebase_server.sock; # for a file socket
+    # server {{ item.upstream_name }}:{{ item.upstream_port }}; # for a web port socket (we'll use this first)
+}
+
+# configuration of the server
+{% extends "core.j2" %}
+
+{% block location %}
+
+    charset     utf-8;
+    # max upload size
+    client_max_body_size 75M;   # adjust to taste
+
+    location /static/ {
+        alias {{ item.static_root }}/; # Project's static files
+    }
+
+    location / {
+        proxy_pass http://etebase;
+
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
+
+        proxy_redirect off;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Host $server_name;
+    }
+{% endblock %}
+
+}