Add loglevel, public setting and config env

* Log levels for less spam when running in production
* Add 'public' setting that allows to not post the invite link for the /help command
* config env variable that allows running multiple instances with different config

config.default.json

@@ -1,10 +1,12 @@
 {
+  "loglevel": "info",
   "http": {
     "port": 3002
   },
   "discord": {
     "token": "<discord bot token>",
-    "client_id": "<discord client id>"
+    "client_id": "<discord client id>",
+    "public": true
   },
   "templates": {
     "bee": {