Rework Config

[Kitt3120]

The current config implementation is very basic and only allows for a config file. But in the future, we want to have environment variables and config file properties combined.

• Create a struct containing all configurable values
• Read from config file and parse into struct
• Read from env vars and parse into struct
• Merge both as one, prioritizing environment variables over config file
• Use the merged one as the config for the bot