Consolidate possibly redundant configuration

`auth.json.example` and `bot.config.json` were originally created with the intent of making tons of settings configurable via these files but that basically didn't happen - environment variables took precendece with the introduction of docker releases and they work arguably better in local dev than config files do.

Instead consolidate these down into a single `.env` file and install dotenv to manage it

Start by comparing auth.json.example and bot.config.json, then trace how the bot currently reads environment variables and configuration. Consolidate the settings into one .env file and use dotenv for loading; done means the redundant configuration files are replaced without losing the existing settings.

Written by the indexing model from the issue text.