Use RenovateBot to update dependencies

[arthurfiorette]

Using some sort of automation to update dependencies of all docker-compose files would be nice, unfortunately github's dependabot doesn't support docker-compose yet (dependabot/dependabot-core#390).

This leaves us with the option to use the Renovate Bot, which I've never used, but from its documentation, it looks simple.

EDIT: I came by reddit ❤️