chore(Docker): add missing environment variables

- `OPENVPN_PROCESS_USER` defaults to `root`
- Add `HTTPPROXY_STEALTH=off`
- Add `HTTP_CONTROL_SERVER_LOG=on`

Dockerfile

@@ -90,7 +90,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     OPENVPN_FLAGS= \
     OPENVPN_CIPHERS= \
     OPENVPN_AUTH= \
-    OPENVPN_PROCESS_USER= \
+    OPENVPN_PROCESS_USER=root \
     OPENVPN_CUSTOM_CONFIG= \
     # Wireguard
     WIREGUARD_PRIVATE_KEY= \
@@ -165,6 +165,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     HTTPPROXY= \
     HTTPPROXY_LOG=off \
     HTTPPROXY_LISTENING_ADDRESS=":8888" \
+    HTTPPROXY_STEALTH=off \
     HTTPPROXY_USER= \
     HTTPPROXY_PASSWORD= \
     HTTPPROXY_USER_SECRETFILE=/run/secrets/httpproxy_user \
@@ -177,6 +178,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     SHADOWSOCKS_PASSWORD_SECRETFILE=/run/secrets/shadowsocks_password \
     SHADOWSOCKS_CIPHER=chacha20-ietf-poly1305 \
     # Control server
+    HTTP_CONTROL_SERVER_LOG=on \
     HTTP_CONTROL_SERVER_ADDRESS=":8000" \
     # Server data updater
     UPDATER_PERIOD=0 \