Split off cli into separate binaries (#37)

* 🎨 Split off cli into separate binaries

This commit splits off the cli into 3 binaries:
- agent
- cli
- provider

The provider now is a separate component that can be tested by itself
and have its own lifecycle. This paves the way to a ligher c3os variant,
HA support and other features that can be provided on runtime.

This is working, but still there are low hanging fruit to care about.

Fixes #14

* 🤖 Add provider bin to releases

* ⚙️ Handle signals

* ⚙️ Reduce buildsize footprint

* 🎨 Scan for providers also in /system/providers

* 🤖 Run goreleaser

* 🎨 Refactoring

cmd/provider/main.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"os"
+
+	"github.com/c3os-io/c3os/internal/provider"
+
+	"github.com/c3os-io/c3os/pkg/bus"
+	"github.com/mudler/go-pluggable"
+)
+
+func main() {
+	factory := pluggable.NewPluginFactory()
+
+	// Input: bus.EventInstallPayload
+	// Expected output: map[string]string{}
+	factory.Add(bus.EventInstall, provider.Install)
+
+	factory.Add(bus.EventBootstrap, provider.Bootstrap)
+
+	// Input: config
+	// Expected output: string
+	factory.Add(bus.EventChallenge, provider.Challenge)
+
+	factory.Run(pluggable.EventType(os.Args[1]), os.Args[2], os.Stdout)
+}