Networks: create internal docker network for proxy server

Prepare to use caddy in docker

files/gitea/docker-compose.yml.j2

@@ -12,6 +12,8 @@ services:
       - {{ backups_dir }}:/backups
       - /etc/timezone:/etc/timezone:ro
       - /etc/localtime:/etc/localtime:ro
+    networks:
+      - "{{ web_proxy_network }}"
     environment:
       - "USER_UID=${USER_UID}"
       - "USER_GID=${USER_GID}"
@@ -25,3 +27,7 @@ services:
       - "GITEA__mailer__USER={{ postbox_user }}"
       - "GITEA__mailer__PASSWD={{ postbox_pass }}"
       - "GITEA__mailer__FROM=gitea@vakhrushev.me"
+
+networks:
+  {{ web_proxy_network }}:
+    external: true