Docker deployment, bug fixes and QoL changes

[Creohex]

Hi!
Made some updates to this project and thought others could, perhaps, benefit from it as well.
Here are the changes:

• Added docker support: dockerfile, docker-compose.yml, .env template
  (multi-staged build, with dependency caching to speed up subsequent builds)
• Updated README.md deployment guide (docker, systemd)
• Fixed null-pointer errors when handling discord webhook messages
• (wow->discord): resolve %user token as armory hyperlink
• (wow->discord): resolve ingame character links as armory hyperlinks
• Updated system message filters in wowchat.conf
• Excluded .metals folder in .gitignore (for VSC users)

[Zebouski]

Sorry that I forgot about this. Are you still playing? You could take over as the official project here since I'm not really a dev, I'd archive this and link to you.

All I wish is that I can migrate my guild's wowchat to your project without me having to use docker, is that viable?

[Zebouski]

You should also merge the turtle-wow.org to turtlecraft.gg domain change that someone sent to my repo