:technologist: Use multiple plugins in go-plugin serve config

[blacksails]

We currently have support for using the same binary to act as multiple different mods. This is based on a configfile which tells the mod manager what mods the binary has available. To simplify this we might be able to leverage the builtin support that go-plugin has for serving multiple mods instead. This will reduce the amount of background processes to one entrypoint for a set of bundled mods.

I have not looked into how the discovery works when multiple plugins are added to the go-plugin serve config.

This might also be able to simplify the code which currently lets the rig-operator binary act as multiple mods.

GoDoc for serve config.
https://pkg.go.dev/github.com/hashicorp/go-plugin#ServeConfig