Split controllers into files

[EmilienM]

/kind feature

Describe the solution you'd like Our controllers are doing a lot of things, it'll be nice to have multiple files within the controller package. The files would handle our resources like networks, load balancers, etc. And we would still have one file per controller for the high level loops. This will make review & maintenance easier for us in the long term, I've seen other providers doing it (e.g. CAPZ).