CI: move docker build machinery to the main repo

more details: https://github.com/SoftEtherVPN/SoftetherVPN-docker/issues/4

docker-compose.yaml

@@ -0,0 +1,23 @@
+version: '3'
+
+services:
+  softether:
+    image: softethervpn/vpnserver:latest
+    cap_add:
+      - NET_ADMIN
+    restart: always
+    ports:
+      #- 53:53         #DNS tunneling
+      - 443:443         #Management and HTTPS tunneling
+      - 992:992         #HTTPS tunneling
+      #- 1194:1194/udp #OpenVPN 
+      #- 5555:5555       #HTTPS tunneling
+      #- 500:500/udp   #IPsec/L2TP
+      #- 4500:4500/udp #IPsec/L2TP
+      #- 1701:1701/udp #IPsec/L2TP
+    volumes:
+      - "/etc/localtime:/etc/localtime:ro"
+      - "/etc/timezone:/etc/timezone:ro"
+      - "./softether_data:/var/lib/softether"
+      - "./softether_log:/var/log/softether"
+      # - "./adminip.txt:/var/lib/softether/adminip.txt:ro"