docker: auto-generate node key file

• Improve docker-entrypoint to auto-generate the node key file when it doesn't exist.
• Rename variable DUNITER_INSTANCE_NAME to DUNITER_NODE_NAME (the former is still accepted though)
• Add optional variable DUNITER_PUBLIC_ADDR to configure the '--public-addr' duniter option

docker/compose/gdev-mirror.docker-compose.yml

 # This is a docker template for running a gdev mirror
-# You should write a .env file aside with the environment variables:
-#
-# --- .env ---
-# SERVER_DOMAIN=gdev.example.com
-# PEER_ID=1234XxxXXxxXxxxXxzbQqEkEpTPxD9S1PtpzkZSYoueyERA5vVtQ
-# ------------
-#
-# The peer id has to be replaced withe the output of the following command
-#
-# >>> PEER_ID >>>
-# docker run --rm -it --entrypoint duniter -v $PWD:/var/lib/duniter/  duniter/duniter-v2s:v0.4.0 key generate-node-key --file /var/lib/duniter/node.key
-# <<<<<<<<<<<<<<<
 
-version: "3.4"
+version: "3.5"
 
 services:
   duniter-rpc:
@@ -37,8 +25,7 @@ services:
       - "/var/lib/duniter/node.key"
       - "--public-addr"
       # SERVER_DOMAIN should be replaced by a domain name that point on your server
-      # PEER_ID should be replaced by the output of the command given at the top of this file
-      - "/dns/${SERVER_DOMAIN?SERVER_DOMAIN should be set}/tcp/30333/p2p/${PEER_ID?PEER_ID should be set}"
+      - "/dns/${SERVER_DOMAIN?SERVER_DOMAIN should be set}/tcp/30333/ws"
       - "--rpc-cors"
       - "all"