Latiosu feat/docker

[lighta]

• Addressed Issue(s): None
• Server Mode: Both
• Description of Pull Request:
  Adds an easy way for developers new to rAthena to get a local development environment up and running with only a single pre-requisite (Docker Desktop).

Instructions for use:

1. docker-compose up -d to spin up database (automatically imports /sql-files/*.sql on first load)
2. docker exec -it rathena bash to connect to lightweight linux container with all rathena dependencies (plus gdb)
3. Devs can now run usual commands (./configure, make, etc ...) or start server (./athena-start, gdb map-server, etc ...)
4. docker-compose down to free resources when done

Demonstration: https://terminalizer.com/view/c05443023904

Additional Information:

• Database is persisted to local disk so no need to recreate database every time.
• First time the database volume is created, all *.sql files are imported into the database. This does not happen on future start ups unless the volume has been deleted (devs can delete volume with docker-compose down --volumes)
• Devs can inspect state of containers with docker-compose ps and modify the setup as they see fit (Official Docs: https://docs.docker.com/compose/compose-file/)

[lighta]

@latiosu updated with minor changes

[Normynator]

lgtm!