feat: add plugin system

[Creaous]

It would be useful to implement some sort of plugin system that allows owners of Nexirift Spark servers to extend the functionality without modifying core files.

Ideally, we would like the plugin system to allow for the following:

• Add, modify or delete GraphQL queries and mutations.
• Add or modify the server start up functionality.
• Add or modify various libraries (under /lib/).
• Modify authentication methods (i.e. add Keycloak).
• Run custom Drizzle database migration files.